CONCLUSIONS I I I 



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." 



Note to P. 78. — Oligotrema, Bourne (Quart. J. Micr. Sci. xlvii. Pt. ii. 

 1903, p. 233), a Molgulid from tlie Loyalty Islands, has a reduced branchial 

 sac and greatly developed pinnate, musc^ilar branchial lobes, probably xised 

 in capturing food. 



