524 ALFRED C. HADDON. 



E n 1 p r c t a . 

 The larval gemmation of Pedicellina is, for convenience 

 sake, noticed a few pages further on. 



Ectoproct a — G ymnolaemata. 

 At the stage of thirty-two segmentation spheres the archen- 

 teron is formed by the invagination and subsequent sub-division 

 of four (Barrois) or eight (Repiachoff ) middle cells of the oral 

 surface, but it does not appear that this archenteron is ever 

 functional, and there is every probability in favour of the view 

 that this functionless organ gives rise to a bud, the so-called 

 "dorsal organ" ( = ' pharynx' of Barrois), as the archenteron 

 in Pedicellina has been shown to do by Hatschek (see below, 

 p. 531). It is worth noticing that ''according to Hatschek it 

 develops as a solid outgrowth of the hypoblastic walls of the 

 mesenteron shortly before the mesenteron joins the oesophagus 

 (fig. 129, B, x)^' p. 244. "A nearly similar organ to this is 

 found in the embryo of Loxosoma [Vogt, 6, and Barrois, 1*]. 

 Here, however, it is double, and forms a kind of disc connected 

 with two eye spots," p. 245. 



The greater part of the internal organs of the larva now de- 

 generates and forms a nutritive or yolk-mass. " The skin of 

 the larva after these changes gives rise to the ectocyst or cell 

 of the future polype. The future polype itself appears to 

 originate, in part at any rate, from the so-called dorsal 

 organ." 



'^ The first distinct rudiment of the polype appears as a white 

 body, which gradually develops into the alimentary canal and 

 lopho])hore. While this is developing the ectocyst grows rapidly 

 larger, and the yolk in its interior separates from the walls and 

 occupies a position in the body cavity of the future polype, 

 usually behind the developing alimentary canal. According to 

 Nitsche it is attached to a protoplasmic cord (funiculus) which 

 connects the fundus of the stomach with the wall of the cell. 

 It is probably (Nitsche, &c.) simply employed as nutritive 

 material; but, according to Barrois, becomes converted into 

 muscles, especially the retractor muscles." 



