12 M. E. lliickol 01) the Oi'(/aniz(i(ion of Sj>ongcs. 



aperture of the pertoctly simple stomaclial cavity is tlic osculuin 

 ur mouth, are of peculiar importance. Sucli a sponge without 

 cutaneous jiores, and the entire ca'lentcric canal-system of 

 Avliich consists, as in Jfi/(/ni, of a perfectly simple stomachal 

 cavity a\ ith a simple mouth-oriiice, was believed by ^Nliklucho 

 to be presented in his (luanchd Idanca. I have, however, by 

 subsctjuent careful examination of the forms of Guancha col- 

 lected byMiklucho himself and handed over to me, ascertained 

 that this sponge possesses simple cutaneous pores. On the 

 other hand, I have examined two microscopically small, but 

 yet perfectly developed (/. e. ovigerous), calcareous s])ongC3 

 collected by me in Naples, in which there are actually no 

 traces of cutaneous pores. The entire body of these most pri- 

 mitive forms of Calcispongiffi consists of an elongate rounded 

 sac (stomach), with a single opening (mouth) on that extremity 

 of the body which is opposite to the point of attachment. For 

 this extremely interesting primitive form, which must evi- 

 dently open the series of the Calcispongia^, I propose the name 

 of Prosifcum. 



But full light is thrown upon these, as upon all other organic 

 relations, only by developmental history. The earliest young 

 fomis of the sponges, the ciliated embryos, which afterwards 

 swarm about freely as larvse by means of their ciliary' coat, dif- 

 fuse this light in the most desirable manner. I have traced 

 the ontogeny of these youngest forms (which were previously 

 known among the Calcispongise only in Sycuin and Dunster- 

 vilUa) in a number of quite distinct genera, and have by this 

 means an'ived at the following results, which in part confirm, 

 and in part essentially enlarge, the existing observations on the 

 ontogeny of the sponges. 



After the c^^ has been broken up, in consequence of the 

 process of segmentation, into a spherical, mulberry-like aggre- 

 gation of closely adpressed, homogeneous, naked spherical 

 cells, the mulbeny-like embr\-o, by stronger growth in one 

 direction, acquires an ellipsoidal or oval foi-m, and covers its 

 surface with cilia. A small central cavity (stomach) is then 

 produced in its interior ; this extends, and, breaking through 

 at one pole of the longitudinal axis, acquires an aperture, the 

 mouth. 



Either before the buccal orifice of the stomach is pcrforatcHl, 

 or at any rate soon afterwards, the free-swimming, ciliated 

 larva of the calcareous sponges sinks to the bottom of the sea 

 and attaches itself there. The point of adhesion is usually 

 situated at the pole of the longitudinal axis which is opposite 

 to the mouth (aboral pole). The body of the young sj)onge 

 now fonns a simple, elongate rounded, adherent sac, the cavity 



