12 M. E. Hiickel on the Onjanizatlon of Sj)onges. 



aperture of the perfectly simple stomaclial cavity is the osculum 

 or mouth, are of peculiar importance. Such a sponge without 

 cutaneous pores^ and the entire coelenteric canal-system of 

 which consists, as in Hydra^ of a perfectly simple stomachal 

 cavity with a simple mouth-orifice, was believed by Miklucho 

 to be presented in his Guancha hlanca. I have, however, by 

 subsequent careful examination of the forms of Guanclm col- 

 lected by Miklucho 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 sponges 

 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 Avhich is opposite to the point of attachment. For 

 this extremely interesting primitive form, which must evi- 

 dently open the series of the Calcispongias, I propose the name 

 of Prosi/cum. 



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

 relations, only by developmental history. The earliest young 

 forms 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 Calcispongife only in Sycum and Dunster- 

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

 means arrived at the following results, which in part confirm, 

 and in part essentially enlarge, the existing observations on the 

 ontogeny of the sponges. 



After the egg 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 mulberry-like embryo, by stronger growth in one 

 direction, acquires an ellipsoidal or oval form, 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 perforated, 

 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 sponge 

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



