Hyatt.] 136 [March 5 



Phalansterium and Spongomonas (pi. 12), except in being a 

 round mass. Carehesinm and Zoothamnium (pi. xn), which 

 though Ciliata are similarly buried in a structureless blastema or 

 a " Zoocyntium," show that the zooeyntium is a homoplastic 

 structure which cannot be considered as an indication of close 

 affinity between the flagellate cells of Protozoa and those of the 

 Porifera. It is also an acknowledged product of the collared 

 cells and not a cellular mesoderm or its homologue. 



The figure of Desmarella moniliforme (pi. 11, f. 30), a free 

 floating colony of eight zoons with collars and flagella, is very 

 similar to Clarke's figure of an isolated fragment of the endoderm 

 of Ascaltis, and seems to us more nearly allied to a sponge than 

 any other Kent has figured, since this has no zoocynctium and 

 the zoons lying side by side have more nearly the relation and 

 aspect of a true membrane. 



Flagellate colonies like Proterospongia may be considered as 

 remotely foreshadowing the ciliated larva of a sponge;. and possi- 

 bly the blastema or zoocyntium may be the homologue of the 

 structureless jelly which filled the blastocoel, and in this sense 

 their characteristics seem to argue strongly for the derivation of 

 the Porifera from the Choanoflagellata as the stock forms of Met- 

 azoa. The figure of Desmarella appears to us to have a similar 

 meaning as regards Biitschli's placula and strengthens the theory 

 of the derivation of the essential characteristics of the monopla- 

 culate embryo of the Calcispongiae from similar flat colonies of 

 single layered Protozoons. The Monoplacula may have been a 

 synamoeba, and the Desmarella merely a homoplastic colony, 

 but it shows that collared cells may arise in a colonial form, 

 which is similar to that of a true membrane and in which the cells 

 adhere without the aid of a zoocyntium or enclosing blastema. 



Huxley was the first author, who realized the great differences 

 between the Porifera and the remainder of the Metazoa. He des- 

 ignated them (Quart Journ. Micr. Sch, 1875) as Metazoa Poly- 

 stomata in contrast with the Metazoa Monostomata, which 

 included all the remaining Metazoa. Though we have on several 

 occasions criticised this view, we are now glad to be able to 

 retract, and even to reinforce Huxley's opinion with the theory 

 of the peripheral growth of vases and oscula in sponges. Ecto- 

 dermal invaginations are shown in the process of formation, in 



