A SKETCH OF HIS LIFE 33 



tor of the hydromedusse was a solitary free-swimming hydra or 

 actinula with no medusa-stage but probably with the power to 

 multiply by budding. Finally, however, becoming more perfectly 

 adapted to a swimming life it was converted into a medusa with 

 pulsating bell, and with sense-organs. After this the larva derived 

 an advantage through attachment, and thus the hydroidr stage 

 was secondarily produced, and then perpetuated through natural 

 selection. It may be said of this theory that while it has gained 

 no important following, yet nevertheless it has never been dis- 

 proven. It is logically sound, presents the direct development of 

 certain medusae from a new point of view, and the future may pos- 

 sibly show that it rests on a basis of truth. 



Researches on the Mollusca and the Molluscoidea. 16 Two of 

 Brooks' first papers deal with the lamellibranchs, one (1874) 

 with an " organ of special sense" in Yoldia, while in the other 

 (1875) the development of Anodonta implicata is described in out* 

 line, and the conclusion is reached that the larva, Glochidium, is 

 a specially modified stage and has no bearing on the question of 

 the origin of the group. In a paper " On the Affini ties of the Mol- 

 lusca and Molluscoidea" (1876) he again approached phylogenetic 

 problems, and concluded that the Brachiopoda have been derived 

 from Vermes, Polyzoa from Brachiopoda, and the molluscan 

 veliger (prototype of the Mollusca) from Polyzoa. Later in his 

 paper on the development of Lingula (1879) he held that the Roti- 

 fera, 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 on the Early Stages in the Development 

 of Fresh- Water Pulmonates" (1879) he observed the rhythmical 

 nature of the process of cleavage, and devoted considerable atten- 

 tion to the origin of the germ layers, to the fate of the blasto- 



16 Professor G. A. Drew, University of Maine. 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 9, NO. 1. 



