90 SPONGES 



system. We have seen that all the forms of canal system originate, in 

 tlieory, if not in fact, by a foldinj,' of the wall of the original {Jlynthus^ 

 and that the Hagelhited chambers represent primitively diverticula of the 

 body wall. Haeckel interprets this folding as a ]n-oces3 of bud-formation, 

 each fold representing a distinct individual, comparable to the original 

 Olynthas from which it arose. In this way an Olynthus becomes in 

 Ascuns divided up by a process of gemmation into a number of incompletely 

 separated individuals, united by a common osculum, and each diverticulum 

 represents a l>ud, capable of becoming a new individual. A Sycon is an 

 Dhjntlius which has undergone strobiloid gemmation, each radial tube being, 

 as it were, a replica of the original Olynthus. At first (1872) Haeckel 

 <lid not extend this theory beyond the second tyjie of canal system, as seen 

 in Sycons, and considered in the case of the third type (Leucons) that the 

 canals arose simply by branching of the pores of an Olynthus with a greatly 

 thickened wall. Hence in Leucons the osculum alone was supi)Osed to 

 be the mark of individuality. But since it was abundantly proved that 

 the chambers in the third type of canal system were strictly homologous 

 with those of the second type, Haeckel later (1889) extended this theory 

 to Leucons and other sponges. In all alike the flagellated chamber was 

 regarded as the individual produced by budding and comparable to a 

 diverticulum of an Ascon or to the whole of an Olynthus. 



In considering this view we may first take it as proved, not only that 

 the tlagellated chambers of the second and third types are strictly homolo- 

 gous one with another, but also that they are perfectly comparalde with a 

 diverticulum uf an Ascon (.see above). Any interpretation, therefore, of 

 the morphological nature of the one applies also to the other. That 

 being so, we may limit the scope of our inquiries to a consideration of 

 the question, how far the diverticula of Ascons can be considered as 

 buds. It is certainly true that each such diverticulum may grow out to 

 form a new individual, with its own osculum. The question is, whether 

 the diverticula in all cases are to be regarded as reduced buds, developed 

 from the first as such, or whether, on the contrary, an outgrowth repre- 

 senting a simple fold of the body wall, may not have taken on the 

 functions, so to speak, of a bud, i.e. of producing new individuals. The 

 answer given will dejjend entirely on the theoretical conception adopted 

 as to what constitutes budding, but it certainly seems a more natural and 

 less strained interpretation of the facts to regard the diverticula simply 

 as the result of a process of growth which results in the first instance in 

 an extension of the body wall and an increase of the absorptive surface, 

 and which may lead, in Ascons, to the formation of new individuals, but 

 which in Sycons and other spongee does not, as a rule, do so. The 

 gemmation theory leads in Ascon.s to a very artificial conception of the 

 morphology of the sponge in cases where the diverticula anastomose into 

 a network, as in t'lathrinidac. Such a form as Clathrina rdicnlum 

 (Fig. 6), for instance, would then represent many thousands of individuals. 

 It seems more reasonable, therefore, even in Ascons, to reject the view 

 that the diverticula of the body wall arc to be regarded jtrimarily as buds. 

 In Svcons and Leucons this reasoning apjdies with even greater force, and 

 we are unable therefore to accept Haeckel's theory of sponge individuality. 



il 



