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 hydroid 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 medusse 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 MolluscoideaJ^ 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 Affinities 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 Vehger 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- 
Professor G. A. Drew, University of Maine. 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 9, NO. 1. 
