22 



BRYOZOA ECTOPROCTA. 



ffl 



sharply bent round towards the middle line of the body. The shell- 

 valves meet at this point like pincers. Near the lower aperture (the 

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

 prominence (r) covered with 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 can be withdrawn into it.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 EHRENBERG and HATSCHEK, 



tl}re is a single com- 

 plicated ring, forming 

 many coils, but 

 CLAPAREDE and 

 SCHNEIDER, whose 

 view has been adopt- 

 ed by PROUHO, think 

 they can distinguish 

 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 first, in the 

 anterior angle, a cell- 

 mass provided with 



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

 EEPIACHOFP, 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 (?) by fibrous strands (/), some of which have 

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



Cyphonautes has a fully-developed and functional alimentary canal. 

 The oral aperture (m) 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 body-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.] 



FIG. 8. Larva of Membranipora Cyplionautes (combined from 

 the figures of CLAPAREDE, SCHNEIDER, and HATSCHEK). 

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

 form organ (o) and the retractile disc (r) m, mouth ; 

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

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



