STRUCTURE AND DEVELOPMENT OF LOXOSOMA. 323 
ever (Nitsche, 4), it is in many parts lined by a distinct 
ciliated epithelium. It is not impossible, however, to regard 
this as merely an advance on the condition found in F lustra, 
as the result of an increased differentiation of certain cells 
situated between body wall and gut, instead of supposing that 
it represents an archaic character, which we see in various 
stages of degeneration in other Polyzoa. On this hypothesis, 
the cilia would have arisen in order to provide a means for the 
circulation of the body fluids. Lankester has described a body 
cavity in Rhabdopleura, although it is far less pronounced 
than in the Oymnolsemata. The question arises, how far 
can Rhabdopleura and Cephalodiscus (35 and 49) be 
considered archaic forms ? In the characters of the budding 
processes, these genera show a very slight amount of complica- 
tion, Cephalodiscus being solitary, and producing paired 
buds from the end of the stalk, whilst the branching of R h a b d o- 
pleura is of a simple nature compared with that of many 
Ectoprocta. In certain features these forms are more 
modified than the Entoprocta; it is probable that the 
arrangement of their tentacles is less primitive than in Loxo- 
soma; the existence of a mesoblastic skeleton (vide Lankester) 
and the character of the tu barium are again features in advance 
of those of the Entoprocta. The occurrence of a pair of 
eyes in the adult Cephalodiscus is a fact of considerable 
interest; the eyes are borne on an organ which is stated to be 
an ovary, and M’Intosh (35) suggests that this will be found to 
be the nature of the dorsal organ of the Entoprocta! In 
Rhabdopleura no retraction of the tentacles is possible, 
and the body cavity can hardly have the origin which has been 
suggested for that of the Ectoprocta. 
It will be difficult to determine the relation of Rhabdo- 
pleura to the other Polyzoa until we are able to learn 
something of the embryology of this form. 
As a result of the foregoing considerations, it appears to 
me that in order to understand correctly the phylogeny of the 
Polyzoa, we must derive the group from a Trochosphere- 
like organism, and that the Entoprocta have remained 
