XVI. ON THE MORPHOLOGY AND SYSTEMATIC POSITION OF 



THE SPONGIDA 1 . 



PROFESSOR SCHULZE'S* last memoir on the development 

 of Calcareous Sponges, confirms and enlarges MetschnikoflTs 8 

 earlier observations, and gives us at last a fairly complete history 

 of the development of one form of Calcareous Sponge. The 

 facts which have been thus established have suggested to me a 

 view of the morphology and systematic position of the Spongida, 

 somewhat different to that now usually entertained. In bringing 

 forward this view, I would have it understood that it does not 

 claim to be more than a mere suggestion, which if it serves no 

 other function may, perhaps, be of use in stimulating research. 



To render clear what I have to say, I commence with a very 

 brief statement of the facts which may be considered as estab- 

 lished with reference to the development of Sycandra raphamts, 

 the form which was studied by both Metschnikoff and Schulze. 

 The segmentation of the ovum, though in many ways remark- 

 able, is of no importance for my present purpose, and I take up 

 the development at the close of the segmentation, while the 

 embryo is still encapsuled in the parental tissues. It is at this 

 stage lens-shaped, with a central segmentation cavity. An 

 equatorial plane divides it into two parts, which have equal 

 shares in bounding the segmentation cavity. One of these 

 halves is formed of about thirty-two large, round, granular cells, 

 the other of a larger number of ciliated clear columnar cells. 

 While the embryo is still encapsuled a partial invagination of the 



1 From the Quarterly Journ. of Microscopical Science, Vol. xix, 1879. 



2 " Untersuchungen iiber d. Bau u. d. Entwickelung der Spongien," Zeit. f. wiss. 

 Zool. Bd. xxxi. 1878. 



3 " Zur Entwickelungsgeschichte der Kalkschwamme," Zeit. f. wiss. Zool. Bd. 

 xxiv. 1874. 



