352 



ZOOLOGY 



SECT. 



species a pair of hollow diverticula, the cells of which contain 

 vacuoles like those of the neighbouring parts of the stomach itself 

 (Fig. 294, C, gl). 



The ectoderm of the process on which the anus is situated 

 subsequently becomes involuted to form a deep pit (Fig, 294, A), 

 and rudiments of the adult tentacles (B, a.ten) are formed as a ring 



A 



m 



aten 



FIG. 294. Actinotrocha larva of 

 Fhoronis, three stages in the meta- 

 morphosis, seen from the side. A, 

 stage in which the rudiment of the 

 involution has appeared. B, stage 

 in which the involution is partly 

 everted. C, stage in which the 

 metamorphosis is almost complete. 

 a. ten. rudiments of adult tentacles] 

 gl. djverticuluui of gastric region ; 

 int. intestine ; inv. ectodermal in- 

 volution ; I. ten. larval tentacles ; 

 pr. I. praj-oral lobe ; st. stomach ; 

 t. tr. circlet of cilia round anus. 

 (From MacBride, after Metschnikoff.) 



of processes at the bases of the larval tentacles. The metamor- 

 phosis from this point is completed with great rapidity. The larva 

 sinks to the bottom ; the pit at the side of the anal elevation 

 becomes everted (B, inv.) and the alimentary canal of the larva is 

 drawn into it (C), the projection thus formed, which grows out at 

 right angles with the long axis of the larva, becoming the body of 



