SPONGES. 61 



the Metazoa, springing from the Protozoa, would sliow similar tendencies toward dif- 

 ferentiation of the colonies. If, as in the sponges, the lower forms had male and 

 female cells in the same body, then the progress of differentiation should lead to a 

 more decided separation of these functions so that some would produce only female 

 and others orjy male cells. In other words, tlie complete sej)aratiou of the sexes would 

 take place by a perfectly natural transition, and we should have male metazouns and 

 female metazoons. 



The sponges are frequently regarded as degraded Metozoa, but to the author this 

 view seems highly improbable. Huxley first recognized the systematic importance of 

 the sponges, but contrasted them as a division with the rest of the Metazoa, while 

 JMacAIlister, and subsequently the author, gave them their true taxonomic rank as an 

 indej)endent branch of the animal kingdom. 



Class I. — CALCISPONGI^E. 



Q'his division is somewhat inappropriately named for the reason that some of the 

 genera have no skeletons, but this objection might, with equal justice, be made with 

 regard to the names applied to the other groups. The animals of this class have fusi- 

 form or cylindrical bodies which may be single with one cloacal aperture, or branching 

 with an aperture at the end of each branch, or more or less solid as in the otlier 

 sponges. When a skeleton is present, the spicules which compose it consist of carbo- 

 nate of lime, and their longer axes are arranged in lines parallel with the canals, that 

 is at right angles to the inner and outer walls of the sponge. 



OuDER I. — PHYSEMARIA. 



This order contains tlie remarkable genera, Jlaliphysema and Gustrojyhi/sema, 

 wiiich, according to Haeekel, are nearer in form and structure to his archetypal animal 

 form, the gastrula, than are any other adult animals. They are small and vase-shaped 

 in Ilaliphi/sema, while Gastrojyhyserna may have from two to five chambers. There is 

 but one aperture above, and the water is drawn into this by ciliary action. According 

 to Haeekel, the body wall consists of but two layers, the ectoderm and the endoderm, 

 but it is evident that the ectoderm of the German savant can be nothing else than 

 mesoderm, for it is composed of loose cells and intercellular protoplasm, while the true 

 ectoderm of all sponges is a simple pavement epithelium and never a comijound tissue. 

 In Haeckel's figure, the whole interior of HaUsphysema is paved with ciliated cells, 

 among which are interspersed amoeboid cells. Both Haeekel and Bowerbank deny the 

 existence of pores, and it is not likely that even transitory openings would have 

 escai)ed their observation. 



The sti'angest part of the history of the Physemaria is that both Carter and Saville- 

 Kent claim that Hallpliysema is a true jirotozoon, and Kent's figure, which is as 

 sjiecific as Haeckel's, depicts a true foraminifer. These observations render it very nn- 

 I'crtain whether the group should be referred to the sponges or to the Protozoa. 

 G astrophysema may be a true sponge, and we therefore describe the order in this 

 connection. Mr. J. A. Ryder describes as an American representative of the grou]), a 

 curious club-shaped animal with a tough cortex and a <'elhdar interior, under tlie name 

 (kwiuruphysema. 



