III CONCLUSIONS WU ie 
pelagic, and deep-sea, free-swimming and sessile modes of exist- 
ence. In the details of their classification they demonstrate both 
stable and variable species, monophyletic and polyphyletic groups. 
They exhibit the phenomena of gemmation and of embryonic 
fission, of polymorphism, hibernation, alternation of generations, 
and change of function. They have long been known as a stock 
example of degeneration; but in fact they lend themselves 
admirably to the exposition of more than one “Chapter of 
Darwinism.” 
Nore to P. 78.—Oligotrema, Bourne (Quart. J. Mier. Sct. xlvii. Pt. ii. 
1903, p. 233), a Molgulid from the Loyalty Islands, has a reduced branchial 
sac and greatly developed pinnate, muscular branchial lobes, probably used 
in capturing food. 
