628 REVIEW. 



derm " are the amoeboid cells observed long since in the gastral 

 cavity of certain sponges after digestion, which, as in Ascetta 

 clathrus, form such traversing processes, and which I 

 believe, with the older workers, to be collar-cells ; to the 

 amoeboid metamorphosis of which Dendy makes no allusion. 

 In these Australian sponges there appears to occur none with 

 a many-layered endoderm. This structure, observed by 

 Haeckel and since universally discredited, certainly appears 

 in Ascetta clathrus, and — I hope I am not wrong in say- 

 ing — was observed some years ago by Mr. Hardy, of Caius 

 College, Cambridge, in a Leucosolenia found by him at 

 Plymouth. 



Turning to histology, Dendy finds " the ectoderm of the 

 Homocoela agrees precisely with what Schulze has described 

 for Sycandra raphanus." Although this form occurs in 

 the Homocoela, it is in my experience rare. The typical 

 ectoderm (e. g. Ascetta clathrus) I find composed of onion- 

 shaped gland-cells containing a nucleus and granules, and 

 provided with a usually fine duct, the expanded end of which 

 forms the hexagonal area whose boundaries are, in the case of 

 most sponges, all that has been observed. In Ascetta 

 clathrus and blanca almost the whole ectoderm is of this 

 type, and at least a large part of it in Ascaltis cerebrum, 

 Ascandra reticulum, and Ascetta primordialis; on 

 the external surface in Sycandra raphanus, Leucandra 

 asp era (sensu Vosmaer), and a new sponge which I pro- 

 visionally name Sycaltis leuconides (having a Sycaltis 

 skeleton and a Leucon-like canal-system, and thereby neces- 

 sitating a change of classification among the Heterocoela). 

 Making such a statement without details or figures, 1 will 

 add that in 1887 Dr. Vosmaer very kindly volunteered to me 

 permission to quote him as being convinced with respect to 

 the ectoderm of Leucandra aspera. This structure of 

 ectoderm was described and figured by Merejkovsky for 

 Halisarca in 1878 ('Mem. Acad. Petersburg^), by Metsch- 

 nikoff for Ascetta blanca in 1879 (" Spong. Studien," 

 ' Z. f. w. Z.,' 32). Though occurring in one of the latter's 



