o574 L IK EDA : 



ill which this vascular couuiiuiiicatioii is just hcconiiug cstablishtHh 

 But from oI)servatious ou uietauiorphosiup; larvai I have obtaiuecl 

 certain suggestions respecting this process. 



III. Metamorphosis. 



As to the external changes of the larval l)o(ly acconijtaiiy- 

 ing metamorphosis, I have scarcely anything to add to the exact 

 and detailed descriptions given hy Metschxikoff and Wilsox. 

 I will, therefore, confine myself mainly to some anatomical points 

 which have l)een less studied by previous observers. ^ly ol)serva- 

 tions of the metamorphosis were mostly made with the larvie of 

 types A and B which were inost al)undant in the neighi)ourhood 

 of the Station. Sometimes I have ol^served under the microscope 

 the whole course of the phenomenon, the duration of the so-called 

 critical moment being usually not more tlum l.j-2'3 minutes. 



Among the the material obtained with the surface-net we 

 ol'teu lind larva: which carry about th(^ partly evaginated pouch, 

 ImU, these indivitluals can Jiot be said to l»e undergoing metamor- 

 ph(»sis in the strict sense of the term, for tluy may continne the 

 free swinuuing life f()r several days afb-r captnre. Besides, tluy 

 do not show anv jvmarkable change in the inlci'iial organs. In 

 lliem the corpnscles are still in luasst'S, the ne{)hridia preserve 

 their oi'iginal forju and position, while the alimentary canal is of 

 the ordinary form and length. 



When the metamorphosis takes place, the partly evaginated 

 ])oucli protrudes suddenly outwards to its full extent and the 

 alimentary canal is thrown into convulsive contractions. jMean- 

 while the latter, especially its eesophageal and intestinal port- 



