DEVELOPMENT OF FLUSTRELLA HISPIDA. 463 



from its origin, appearance, and position, there can be no doubt 

 is a vestigial stomach (PI. 25, figs. 63 a-6,64,65 a-c,8t.). This 

 supposed stomach is identical in its structure with that de- 

 scribed by Harmer (11, p. 446, PI. XXVII, figs. 1, 2) as occur- 

 ring in the larva of Alcyonidium only, unlike the stomach in 

 that case, communication with the exterior by the pharynx is 

 never established. As is the case also in Alcyonidium, 

 the stomach is lined simply by a protoplasmic mass in which 

 nuclei and numerous yolk spherules are embedded. The 

 lining epithelium shows no trace of any glandular character, 

 and the organ itself remains entirely vestigial and disappears 

 before free life commences. 



In describing the development of the stomach in the 

 Cyphonautes larva, Prouho (21) says : " La depression orale 

 devient de plus en plus profonde, pendant que la region 

 aborale devient de plus en plus conique . . . Les cellules 

 de la masse endodermique, qui se sont un peu multipliees 

 pendant que I'embryon subissait les modifications ci dessus, 

 se desposent autour d'un axe et ferment une masse, pleine, 

 allongee, oblique, dont une extremite vient s'appuyer contre 

 le fond de I'invagination orale ; cette masse endodermique, 

 definitivement rejetee a I'arriere de la larve occupe d'ores et 

 deja la position de futur estomac." 



The organ which has been regarded as the stomach in the 

 larva of Flustrella hispid a has been shown by its origin 

 and position to correspond to the endodermic mass which 

 ultimately gives rise to the stomach in the Cyphonautes 

 larva, and it is also closely comparable to the rudimentary 

 stomach of the larva of Alcyonidium, except for the fact 

 that it never communicates with the phai'ynx. The exceed- 

 ingly slight development of the stomach in Flustrella is 

 easily explained when the short duration of free larval life, 

 and the correlated abundance of the supply of food yolk are 

 taken into consideration. 



According to Prouho (20) the organ which has been here 

 termed the pharynx is to be regarded as a rudimentary intestine 

 much less differentiated than that of Alcyonidium. But, as 



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