56 BRYOZOA ECTOPROCTA. 



is specially marked in the Phylactolaematous Bryozoa (Fig. 28), on 

 account of the horse-shoe-shaped lophophore, the presence of the 

 epistome (ep), and the similarity in the arrangement of the body- 

 cavity. Thus in the latter, we find a septum separating the 

 lophophore-cavity from the rest of the coelom, and having the 

 nephridial funnels* sunk in it, and an epistomal cavity distinct (?) 

 from the lophophore-cavity (cf. Fig. 5, p. 9). The recognition of 

 these points of agreement throws a new light upon the Bryozoa. 

 It shows that the Phylactolaemata represent by far the most primitive 

 type, while the Gymnolaemata, with regard to the segmentation of 

 the lophophore, have undergone simplification, the condition of the 

 body-cavity also showing degeneration. 



Further, through a comparison with Plioronis, the remarkable 

 form of the Bryozoan larva is to some extent explained, and the 

 task of tracing back the Bryozoan larva to the Trochophoran type 

 is rendered easier. The comparison of the Bryozoan larvae to the 

 Actinotrocha has been made chiefly by HARMER (Entoprocta, Lit., 

 No. 4) and OSTROUMOFF (No. 24). 



The forms of Bryozoan larvae in which the larval intestine is 

 retained will be treated first, as the most primitive. Among these 

 forms, Cyphonautes, by the possession of shell-valves and an atrium, 

 shows a secondarily modified condition, the larvae of Tendra and 

 Alcyonidium being most suited for comparison with the larvae of 

 other groups of animals. The most striking organ of the larva is 

 the massive equatorial corona, the locomotory organ. We should 

 be tempted to see in this the homologue of the pre-oral ciliated 

 ring of the Trochophore, but for the difficulty presented by 

 the fact that the circular mantle-cavity which is destined to form 

 the greater part of the body-wall lies in front of the corona. In 

 any case, we are led, by a comparison with the Actinotrocha, to 

 consider the retractile disc, on account of the similarity of its 

 position, as the equivalent of the apical plate. This view, which is 



* The investigations made so far on this point are not conclusive. The 

 nephridia of the Phylactolaemata (see diagram, Fig. 28, n) were first seen by 

 VERWORN, and later were described more in detail by CORI (No. 46), but their 

 occurrence has recently been disputed by BRAEM and KRAEPELIN [also by OKA]. 

 BRAEM connects the structures referred to with his " forked canal" (p. 42). It 

 is, however, not impossible that these organs exist side by side. CORI'S state- 

 ments have, on the other hand, been supported by BLOCHMANN (Brachiopoda, 

 Lit. No. 4). 



HARMER (No. 16) was unable to convince himself of the presence of special 

 excretory organs in the Gymnolaemata, but we may well feel inclined to regard 

 as a nephridium the intertentacular organ observed in some forms by FARRE, 

 SMITT, HINCKS, and more recently by PROUHO (see p. 14). 



