99 



BRYOZOA ECTOPROCTA. 



shai'i^ly bent round towards the middle line of the body. The shell- 

 valves meet at this point like pincers. N'ear the lower aperture (the 

 entrance to the atrium) the valves gape. At the aboral pole, a 

 prominence (r) covered Avith stiff cilia projects from the shell, but 

 can be withdrawn into it. In this we recognise the homologue of 

 the " retractile disc." 



Some uncertainty still prevails as to the ciliated ring that runs 

 round the edge of the bell. According to Ehrbnberg and Hatschek, 



there is a single com- 

 plicated ring, forming 

 many coils, but 

 Claparede and 

 Schneider, whose 

 view has been adopt- 

 ed Ijy Prouho, think 

 they can distinguish 



Fig. 8. — Larva of Membranipora = Cypho)icmtes (comhincA from 

 the figures of Claparede, Schneider, and Hatschek). 

 a, atrium ; an, anal aperture ; /, fibres connecting the pyri- 

 form organ (o) and tlie retractile disc (r); in, mouth; 

 s, glandular thickening (liomologue of the sucker); s', 

 similar, smaller organ (shell-adductor muscle).* 



two distinct rings of 

 cilia, an anterior ring 

 in the neighbourhood 

 of the pyriform organ 

 (o) and a posterior, 

 circum-anal ring, part 

 of which sinks into 

 the atrium. 



On the oral invagi- 

 nated surface we 

 notice lirst, in the 

 anterior angle, a cell- 

 mass provided with 

 a tuft of cilia; this is the pyriform organ (o). According to 

 Repiachoff, two parts may be distinguished in it ; an invaginated, 

 sucker-like epithelial thickening surrounded by a ring of cilia (ecto- 

 dermal furrow), and a cell-accumulation lying above this (the actual 

 pyriform organ). As in Alcyonidium, this organ is connected with 

 the retractile disc (r) by fibrous strands (/), some of which have 

 been claimed as muscle-fibres and some as nerve-fibres (Prouho). 



Cyplwnautes has a fully-developed and functional alimentary canal. 

 The oral aperture (»?) is found in the base of the atrium, and leads 



* [The organs s and s' are not isolated structures as represented in the figure, 

 but are situated underneath the Ijody-wall, which latter should be indicated as 

 a line extending forwards from the anus below s and s' and joining the ciliated 

 ring near the mouth. — Ed.] 



