..I NiYki \ 361 



The larval males make their way into the oesophagus of the 

 female, where they no doubt live for some time, and probably 

 become mature, though the seminal pouch of the adult is not 

 found in many of the males living in the oesophagus. When 

 mature the males leave the oesophagus, and pass into the 

 uterus. 



Phascolosoma. Cilia appear in Phascolosoma (Selenka, 

 No. 309) while the ovum is still segmenting. After segmentation 

 they form a definite band immediately behind the mouth, which 

 divides the larva into two hemispheres a prae-oral and a post- 

 oral. A prae-oral band of cilia is soon formed close to the post- 

 oral band, and at the apex of the prae-oral lobe a tuft of cilia 

 also appears. 



The larva has now the characters of a trochosphere, but 

 differs from the typical trochosphere in the post-oral part of the 

 ciliated equatorial ring being more important than the prae-oral, 

 and in the absence of an anus. 



The metamorphosis commences very early. The trunk 

 rapidly elongates, and the prae-oral lobe becomes relatively less 

 and less conspicuous. The zona radiata becomes the larval 

 cuticle. 



Three pairs of bristles are formed on the trunk, of which the 

 posterior pair appears first, then the anterior, and finally the 

 middle pair: an order of succession which clearly proves they 

 can have no connection with a true segmentation. 



The tentacles become developed between the two parts of the 

 ciliated ring, and finally the prae-oral lobe, unlike what takes 

 place in the Gephyrea armata, nearly completely vanishes. 



The anus appears fairly late on the dorsal surface, and the 

 ventral nerve cord is established as an unganglionated thickening 

 of the ventral epiblast. 



GEPHYREA TUBICOLA. 



The larva of Phoronis was known as Actinotrocha long 

 before its connection with Phoronis was established by Kowa- 

 Icvsky (No. 372). There is a complete segmentation leading to 

 the formation of a blastosphere, which is followed by an invagi- 

 nation, the opening of which is said by Kowalevsky to remain as 



