Text-book of embryology

Front matter

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CORNELL UNIVERSITY LIBRARY

BOUGHT WITH THE INCOME OF THE SAGE ENDOWMENT FUND GIVEN IN 1891 BY

Prefatory Note

THE design of this Text-book of Embryology, of which this is the first volume, is to associate the structural development of embryos with broad generalizations of what is known of their physiology. Attention will be drawn, for instance, to the correlation between the function of certain organs of a larva and its habit of life, and, in a more general way, between function and habit and the course of development. Reference will be made to some of the more striking results obtained by Experimental Embryological research. Attention will be drawn to gaps in our knowledge which indicate promising fields for research.

It is hoped that the interest of all students of Embryology will thus be stimulated, and the practical value of these volumes, especially for students of medicine, ensured.

A second volume, by Professor Graham Kerr, in which the lower Vertebrata will be dealt with, will follow as soon as possible, and a third volume by Mr. Richard Assheton, on Mammals, will complete the work.

The Authors are responsible for the facts and generalizations recorded, and to them is due all the credit which may be given to the work.

THE EDITOR.

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Preface

Tais book has been written in order to achieve two objects, first to place before the reader in as succinct a form as possible the best ascertained results in the field of Invertebrate Embryology, and secondly to indicate some of the problems which as yet remain unsolved and the best means of attacking them.

In order to attain the first object a number of typical life-histories, illustrating all the important groups of Invertebrata, have been described, and in selecting the types for special description two principles have guided us: first, the life-history of the type chosen must be thoroughly ascertained, and second, the type must be a common form easily accessible to students in temperate regions. Thus the spider has been chosen as a type of the Arachnida rather than the scorpion, and for the same reasons the life-histories of parasitic forms have been very slightly dealt with. The Trematoda and Cestoda have been entirely left out of consideration because it is difficult to obtain a complete series of the stages in the life-history of any one species—and though the external features of the life-history of members of these groups are known, their organogeny is still to be worked out. Moreover, the external features of the development of Trematoda and Cestoda are adequately described in ordinary text-books of zoology.

In pursuit of the second object the methods used by the best investigators have been given in connection with the description of the life-history of each type examined by them, and we have ever striven to keep before the mind of the student the idea that the ultimate object of the Science of Embryology is not solely the ascertaining of facts but especially the determination of the laws of ix aera! eee a as Invertebrate Embryology, very much must necessarily be omitted, but it seemed to us better to run the risk of criticism on this score and to bring our survey of the field to a conclusion within a reasonable period, rather than to attempt to give a complete account of all that is known of Invertebrate Embryology. Such an attempt would involve the task of writing not a single volume but a series of volumes; it would require for its accomplishment many years and would be beyond the powers of one man. Moreover, the first volume would be out of date long before the last volume was published.

The literature lists have been purposely kept as brief as possible —as a rule only the most recent papers on the subject have been cited. Where earlier papers have been referred to it is chiefly because these papers, in laying the foundation of our knowledge, have not been superseded by later work.

In conclusion, my best thanks are due to my colleagues, Professor Lefroy and Mr. Dobell, for valuable suggestions, and to my wife for much help in the tedious work of preparing the Index.

Chapter I Introduction

Scope of Embryology—Growth, maturation, and conjugation of the germ-cells—Sex-chromosomes and their bearing on theories of heredity—Recapitulation theory of development and the evidence in its favour—Embryonic and larval phases of development and their mutual relationship——Factors modifying the course of development. . : é é ; : : Page 1

Chapter II Practical Hints

Methods of preserving embryos— Methods of embedding embryo for sectioncutting and of orientating them so that the sections shall be cut in a known direction , : ? : . : ‘ é Page 32

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Chapter III Porifera

The development of Sycandra raphanus as a type of the Calcarea: the Blastula, Amphiblastula, and Ascon stages in its development—The development of other sponges (Oscarella, Plakina, Esperia, Spongilla, Clathrina, Lewcosolenia) — The development of the gemmule of Ephydatia—The ancestral history of sponges . : ; . ‘ F fg . Page 37

Chapter IV Coelenterata

The development of Z'ubularia as a type of the Hydrozoa—The development of the eggs of free-swimming medusae—The development of the gonophore of Tubularia and of the medusa of Podocoryne -- Other gonophores—The development of

. Siphonophora, Narcomedusae, and Trachymedusac—The development of Aurelia asa type of the Scyphozoa—The development of Pelagia—The development of Urticina as a type of the Actinozoa—The development of Actinia bermudensis— The larvae of Zoanthidae and Cereanthidae—The development of Aleyonaria—The development of the skeleton of Caryophyllia—The development of Berée as a type

pal xi INVERTEBRATA of the Ctenophora—The formation of the tentacles of Callianira—The affinities of the Ctenophora with other Coclenterata—The experimental embryology of Coelenterata—The ancestral meaning of the Planula larva. . Page 58

Chapter V Platyhelminthes

The Polyclada the most primitive group of Platyhelminthes so far as their development is concerned—Development of Planocera inqutlina as a type of the Polyclada —The nature of spiral cleavage—Definition of cell-lineage and tlie nomenclature employed—Miiller’s larva in the development of Yungia and its metamorphosis— The interpretation of Miiller’s larva and the light which it throws on the ancestral history of Platyhelminthes . é ; ‘ . Page 102

Chapter VI Nemertinea

The development of Cerebratulus lacteus as a type of the Nemertinea—The Pilidium larva and its metamorphosis—Experimental embryology of the Nemertinea—The interpretation of the Pilidium larva and the light which it throws on the ancestral history of Nemertinea P : 3 : . Page 118

Chapter VII Annelida

Methods of preserving and mounting the eggs of Annelida—The development of Polygordius appendiculatus as a type of the Annelida: its cell-lineage: its Trochophore larva and the metamorphosis thereof—The Trochophore larva of Polygordius lacteus and its metamorphosis—The development of various Polychaeta—The development of the nephridia of Criodrilus—The development of Nephelis as a type of the Hirudinea—The development of Clepsine—The interpretation of the Trochophore larva and the ancestry of the Annelida. Page 128

Chapter VIII Arthropoda

The development of Peripatus capensis as a type of the Prototracheata—The development of Astacus as a type of the Crustacea—The formation of layers in Homarus, Lucifer, and Euphausia as types of the Eucarida—The formation of layers in Mysis as a type of the Peracarida—The formation of layers in Polyphemus and Branchipus as types of the Cladocera—The formation of layers in Lepas as a type. of the Cirripedia—The larval history of Cyclops as a type of Crustacean larval history: the Nauplius and Metanauplius larval stages—The larval history of Phyllopoda: the Nauplius larva of Apus and Branchipus—The larval history of Cirripedia: the Nauplius and Pupa stages—The larval history of Ostracoda— The larval history of Euphausidacea and Penaeidea : the Nauplius, Protozoaea, and

CONTENTS © xiii

Zoaea larval stages—The ancestral meaning of the Nauplius larva—The development of the parasitic Copepod, Actheres ambloptitis, and the support which it gives to the recapitulation theory of development—The Zoaea larva in Euphausidacea, Penaeidea, Caridea, Anomura, and Brachyura—Ancestral meaning of the Zoaea larva—The Mysis larval stage: its modification in the Loricata into the Phyllosoma larva: its modifications among the Crangonidae and Thalassinidae—The Megalopa larval stage of Brachyura—The brephic stages in Anomura—The larval history of Stomatopoda—The Metanauplius, Erichthoidina and Erichthus larval stages—The Alima larva—The larval history of Portwnion as a type of the parasitic Isopoda—The development of Agelena, a type of the Arachnida—The development of Limulus: its Trilobite larva and the significance thereof—The development of the Scorpion and of some other Arachnida—The development of Pantopoda—The development of Tardigrada—The early development of Donacia as a type of the embryonic development*of Insecta—The early development of Doryphora—The embryonic development of Blatia and the supposed origin of its mid-gut epithelium—The development of the genital organs in Phyllodromia— The formation of the embryonic membranes in the primitive Aptera (Lepisma and Machélis)—The metamorphosis of Galerucella ulmi as type of the larval history of Insecta—The development of the wings in Doryphora—The development of the compound eye in Dytiscws—The metamorphosis in various families of Coleoptera, Diptera, and Lepidoptera—The complicated metamorphosis of the Muscidae—The meaning of metamorphosis as exemplified by observations on Bombyx —The development of Scolopendra as type of the Myriapoda—The development of Julus —The ancestral history of Arthropoda . ; : : . Page 169

Chapter IX Mollusca

The development of Patella as a type of the Mollusca—The metamorphoses of Aemaea, Fissurella, and Haliotis—Experiments on the eggs of Patella—The development ‘of Paludina as type for the formation of the internal organs of Gastropoda—The development of Polyplacophora—Methods of preserving and staining the eggs of Gastropoda—Various modes of the development of the velum in Gastropoda— The larval kidneys of Gastropoda and their supposed homologies—The development of Solenogastres—The development of Dentaliwm as type of the Scaphopoda— Experiments on the eggs of Dentaliwn—The effect of cutting off the polar lobes of the egg—The development of Dreissensia asa type of the Pelecypoda—The larval development of the oyster—The development of Yoldia as a type of the Protobranchiata—The mode of development of heart and pericardium in Cyclas—The development of Unionidae—The Glochidium larva—The segmentation of the egg of Sepia as a type of Cephalopod egg-—The development of Loligo as type of the Cephalopoda—The development of the eye of Cephalopoda—General considerations on the ancestral history of the Mollusca F ‘ 3 . Page 291