ZOOLOGY FOR MEDICAL STUDENTS 



CHAP. 



liki- term may make their appearance. These modifications of 



, do with the fact that the Nereis at this stage gives 



n-lrequentin- habit and swims about freely so as to distribute 



Aider area. With the assumption of the pelagic 



:ies about another modification very usual in pelagic 



animals namely a -n-at increase in the size of the eyes. 



In an allied family of Polychaetes, the Syllidae, to which a number 



FIG. 70. 



if M-xual phenomena in the Syllidae 



;,ham, Cambridge Natural History). I, Heterosyllid ; 



hiimata ; III. and IV, Autolytus ;V,A. edwardsii, 



-.nal individual; B, C, D, E, sexual 



stage in development of a sexual 



mion marine worms belong, there occur similar modifications, 



rurrird in nuidi further than in Nereis. In the simplest 



. I) what takes place is very much the same as in Nereis, 



isyllid condition beinu assumed in which the hinder part of the 



MID- the ^amclrs takes on an appearance markedly different 



1 tlu- front part. In exceptional species of Syllis (S. Jianmta) 



.Hid condition has been reached there makes its appear- 



