270 N. Annandale : Notes on Freshwater Sponges. [Vol. I, 



because none of his sections passed through them. If, however, a 

 small piece of the sponge is teased up, stained with hsematoxylin, 

 cleaied and mounted, it is not difficult to see the structures I have 

 alluded to, although this method of observation does not perm.it of 

 a minute examination of the cell anatomy. I have found closeh' 

 similar embryos in Spongiila carieri both in summer and in spring, 

 and also in an indeterminate sponge (probably an Ephydatia) taken 

 by Mr. H. C. Robinson and myself at Biseiat in the Siamese Malay 

 States in autumn. I am indebted to Dr. Evans for the oppor- 

 tunity of re-examining, in a critical manner, the latter specimen, 

 which I had handed over to him before I took up the study of the 

 freshwater sponges m3^self. 



IV. — The Nature of the Pores in Spongiila. 



Th'^ exact nature and origin of the external apertures of the 

 inhalenl canals in the Demospongia has been much disputed. 

 Several authors claim to have established the fact that these 

 apertU'.es are intracellular and that the cells which cont?in them 

 are porocytes homologous with those of the Calcarea. This view 

 has been opposed b}'' Minchin and others on theoretical grounds. 

 An examination of fresh and well preserved specimens of the 

 species of Spongiila occurring in Calcutta has convinced me that 

 the structure of the pores is variable even within the limits of 

 this genus. Two types can in fact be distinguibhed in the species 

 examined, while from the descriptions of other species it seems 

 probable that they also exemplify one or other of these t^^pes. 

 Before describing the different forms of pores it will be as well 

 to state the methods of investigation adopted. I find that in a 

 tropical climate the best preservative for the dermal membrane 

 is absolute or nearly absolute alcohol. The cutting of serial 

 sections is not a satisfactory method of investigating this part 

 of the sponge under any conditions, and in a climate such as that 

 of Calcutta is almost impossible. If the dermal membrane does 

 not adhere closel}^ to the parenchyma, a piece of it may be de- 

 tached with a pair of needles, floated off, stiined — I find Ehrlich's 

 acid ha?matoxylin an excellent stain — and mounted for examina- 

 tion. In mam^ species, however, it is difficult to remove a large 

 enough piece of the memibrane in this wa}^, and in such cases I 

 find the best method is to shave the surface of the hardened sponge 

 with a sharp razor. A portion of the parenchyma usually adheres 

 to the membrane thus removed, but this does not very much 

 matter, as sufficient clear spaces remain for the purposes of 

 examination. 



The first type of pore is found in those species (e.g., S. carten) 

 in which the subdermal space is small and the pores correspond in 

 position more or less exactly with the distal extremities of the 

 canals. Such species have comparatively large pores and as a rule 

 there is no projecting collar round the osculum. The pores are 

 simply gaps in the membrane, being surrounded by cells which 



