66 



there is an opening between the zooecium and the ooecium in the separating wall, 

 but I "must dispute its presence, as I have always by transverse grinding found 

 the separating wall unbroken. Calvet has found an ooecial operculum with two 

 layers, which is opened by a muscular apparatus. 



5) The double-valved ooecia (PI. VII, figs. 3 a, 3 h, 3 i, 3 j, 3 k, 3 1) which 

 have hitherto only been found in Alysidhim parasiticum, consist of two double 

 layered, arched valves, the edges of which meet together and with the zoceciuni 

 bearing them form a bean-shaped body. They rise from zooecia, the oral surfaces 

 (PI. VII, 3 c) of which form nearly a right angle with the longitudinal axis of 

 the zooecium, and the two valves arise in the lateral borders of the said surface 

 on each side of the zooecial aperture, which leads directly into the bottom of the 

 ooecium. As each of the two hollow valves has an inner connection with the 

 zooecium through a pore-chamber, we must regard them as two kenozocEcia (see 

 under Alysidium parasiticum). 



6) The acanthostegous ooecia. We indicate by this name the cavities found 

 in the two Electra species, E. zostericola (PI. IX, fig. 2 b) and E. (Heteroecium) 

 amplectens (PI. IX, figs. 1 a, 1 c), which externally are limited by two rows of 

 hollow spines meeting together in the middle line of the frontal surface. The 

 ooecial cavity in E. zostericola is bounded internally by the frontal membrane of 

 the zooecium, and externally by the mentioned spines, and according to Ostrou- 

 moff this cavity contains developing larvae. While the zooecial operculum in 

 the species mentioned is placed at the distal end of the ooecium-bearing zooecium, 

 in the corresponding zooecia of E. amplectens it is situated proximally to the 

 area formed by spines, and as this species has only been examined in dried 

 condition, nothing is known as to how far the ooecial cavity also here is bounded 

 in the same way as in E. zostericola. 



Before leaving this subject, we may briefly touch upon the question of the 

 egg's transference into the ooecium. The older view that the egg is carried from 

 the zooecium (or gonozooecium) into the ooecium through an inner connection 

 seems according to JuUien's investigations to hold good for Hippothoa hyaliha, 

 in which species the gonozooecium and the ooecium form a common cavity, 

 closed by a common operculum. According to Jullien^ the zooecium has no 

 polypide but contains an ovary, and he supposes that the tentacular sheath is of 

 service to the egg by carrying it over into the ooecium. A similar direct trans- 

 ference probably occurs also in all the cases where endoooecial ooecia are present 

 with an operculum in common with the zooecium (Hippothoidae, Calenariidae, etc.). 



». 90, p. 19. ^ 45, p. 31. 



