WILLIAM KEITH BROOKS — CONKLIN 



tunicates, for it deals in original and philosophical manner with 

 such problems as the origin of chordates, the origin of pelagic 

 animals, the discovery of the ocean bottom, and the effects of 

 this upon the evolution of life. 



Another major line of his work was on the anatomy and 

 embryology of the Mollusca. One of his first papers was on 

 "An organ of special sense in the lamellibranchiate genus 

 Yoldia," this sense organ being a long retractile tentacle, half 

 way between the siphon and the lower edge of the mantle on 

 the right side. This paper was soon followed by one on "The 

 embryology of the fresh-water mussels," in which the entire 

 development of Anodonta implicata is described in brief out- 

 lines, and the conclusion is reached that the larva, or glo- 

 chidium, is a specially modified stage, adapted to a special pur- 

 pose, and having no bearing on the question of the origin of 

 the group. Both of these papers are brief abstracts of three 

 pages each, and they were read at the meetings of the Ameri- 

 can Association for the Advancement of Science in 1874 and 

 1875. I n a paper "On the affinities of the Mollusca and Mol- 

 luscoida" (1876) he concluded that Brachiopoda have been 

 derived from Vermes, Polyzoa from Brachiopoda, and the 

 Molluscan Veliger (the prototype of the Mollusca) from Poly- 

 zoa. The Lamellibranchiata he held to be a side branch, and 

 not ancestral to the group of mollusks as a whole. Later 

 (1879), m ms paper on "The development of Lingula and the 

 systematic position of the Brachiopoda," he held that the 

 Rotifera, Polyzoa, and Veliger were three branches which 

 early diverged from the vermian stem. The Brachiopoda he 

 held to be the most highly specialized members of the polyzoan 

 branch, the Mollusca the most highly specialized of the Veliger 

 branch. For these three branches he proposed the name 

 Trochifera. 



In his "Observations upon the early stages in the develop- 

 ment of the fresh-water pulmonates" (1879) he observed the 

 rhythmical nature of the process of cleavage, the formation of 

 the ectoderm from the clear cells at the animal pole of the egg, 

 the formation of the endoderm from the macromeres at the 

 vegetative pole, and the lack of a continuous mesodermal layer 

 in the embryo. He devoted particular attention to the fate of 



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