Studies on Sponges. 441 



Now that we know the anatomy of Velinea we can pass to the 

 study of the tissues. As iu all kuown Sponges the mass of the body 

 consists of couuective tissue, inclosed by epithelium. The whole outer 

 surface is covered by flat epithelium-cells. The centra of these eells are 

 rather far one from another (fig. 3) ; this makes the layer resemble 

 the ectodermal epithelium oi Si/cmicha rapha7ius^. I could not see 

 distinct limits between these cells and so I was not able to decide whether 

 there is a rather hyaline plasma in the outer parts of the cells and a 

 granular part aggregated around the nucleus in the centre of the cells, 

 or whether the cells consist solely of the granular part lying in a 

 copious secondary substance, secreted by the cells. A comparison with 

 the epithelial layer of other Sponges, for instance Sijcandra^ would be 

 an argument in favour of the first view ; but it ought to be remembered 

 that the limits of the granular mass is in our sponge much more distinct 

 thau in Sycandra according to Schulze's pictures. This, and the fact 

 that the hyaline substance stains very little, are on the contrary argu- 

 ments of the latter view. Fresh material is wanted for deciding this 

 question. 



The same kind of epithelial cells seems to line all efiferent and 

 afferent canals. Some of the lacunae in the spongeous soft mass, that 

 is in the cloacal tubes are perhaps without this epithelium ; at least 

 there was frequently no trace of it at all. In flg. 10 I have drawn 

 some cells of the epithelium lining the cloacal tube. As I have said those 

 of the external layer do not ditfer from them, they are more or less oval- 

 shaped, possess many highly refringent granules and a round or oval 

 nucleus with finer granules and a darkly staiued nucleolus. The collar 

 cells have no peculiar character, except their small size. The conuective 

 tissue consists of ahyaline mass in which are to be seen beautiful granulated 

 cells with long branching processes, by means of which they are hanging 

 together in order to form a fine network (fig. 14) . The nuclei are not very 

 conspicuous. Very often vacuoles are visible. These ordiuary cells of 

 connective-tissue assume different shapes. In the deeper parts the pro- 

 cesses are more numerous than in the parts nearer the canals. There 

 the majority are spindle-shaped. In fig. 14 I have joined together some 

 typical forms that ali occur in the deeper parts. In some places they are 

 more contracted, as in fig. 15. I cannot say whether these have auother 

 function or not. Somethiug like spongoblasts I have not found; nor 

 could I detect eggs or spermatozoids. Nothing of the curious sperm- 



1 See F. E. Schulze, Zeitschr. f. wiss. Zool. XXV. Suppl. Bel piate XIX. 



