CONTENTS. VU 



tinuous origin of whole central nervous system from ectoderm, 60. The 

 cerebral grooves, 61 . The eyes, 61. The tentacular nerves, 62. 

 Cerebral invaginations in other types, 62. Summary of early develop- 

 ment of central nervous system, 63. The stomodseal and proctodseal 

 ingrowths, 64, 67. The slime glands, 64. The endoderm, 65. Partial 

 closure of blastopore, 66. Separation of endoderm from ectoderm, 66. 

 The mesoblastic bands and somites, 68. 



CHAPTER IV. 

 Changes from stage A to stage F {continued). The somites and 



BODY CAVITY. pp. 73 — 98. 



Ccfilom or enterocosle; pseudocoele or vascular space, 73. Summary 

 of results on development and fate of ccelom and vascular sj)ace, 73. The 

 history of the 3rd somite, 75. Thickening of its side walls (parietal 

 mass), 76 ; cavity in the parietal mass, 76. Dorsal extension of somite, 

 77. Increase of cavity of parietal mass, 77. Opening of somite to 

 exterior, 77. Summary of 3rd somite, 77. Branched cells of vascular 

 space, 78. Comparison between the vascular space and the blastoccele of 

 other types, 78. Division of the somite into a dorsal and ventral 

 division, 78. Fate of ventral division — salivary gland, 79. Salivary 

 gland a nephridium, 79. The body cavity and vascular system, 82. 

 Origin of heart and various parts of body cavity, 83. The pericardial 

 cavity, 85. The body cavity is a vascular space, 85. The somites of 

 the preoral lobes, 86. The somites of the jaws, 88. The somites of the 

 fourth to the fifteenth pairs, 90. Somites of the sixteenth to the twen- 

 tieth pairs, 93. The generative organs, 93. The germinal nuclei, 94. 

 Somites of twenty-first pair as generative ducts, 95. Receptaculum 

 ovorum of West-Indian species, 97. 



CHAPTER V. 



General considerations on the development dp to stage F. 



pp. 99—124. 



Ovum originally much-yolked, 99. Comparison with mammalian 

 ovum, 100. Cleavage on centrolecithal type, 101. Cleavage of centro- 

 lecithal ova not a complete cleavage, 102. Complete cleavage, 103. 

 Discussion as to whether complete or incomplete cleavage is the most 

 primitive process, 103. Complete cleavage not suggestive of colonial 

 Protozoon ancestry, 104. Suggestion that the ancestral metazoon was a 

 multinucleated Protozoon, 106. Metschnikofif's views as to origin of 



