STUDIES ON THE COMPARATIVE ANATOMY OE SPONGES. 215 



which I have examined very numerous species. Therefore, 

 even if we admit that perforated prosopyle cells occasionally 

 occur, there is no reason for believing that this is the usual 

 condition, but quite the contrary. When viewed en face the 

 prosopyles of calcareous sponges usually appear as sharply 

 defined approximately circular spaces (figs. 25, 30). Not 

 infrequently the nucleus of an ectodermal epithelial cell 

 happens to lie exactly on the margin of this space (fig. 30), but 

 I do not think there is any reason for regarding this fact as 

 indicating that the prosopyle itself is of an intra-celiular 

 nature; while sections such as those figured by Schulze in the 

 case of Sycon raphanus, and by myself in the case of 

 Grantia labyrinthica, clearly indicate the contrary. 



Before leaving the question of the ectoderm I may con- 

 veniently describe in this place a very curious condition which 

 exists inGrantiopsis cylindrica (4). This highly interesting 

 Australian species is known only from a few fragments, 

 probably all belonging to the same specimen. These fragments 

 are, however, in a remarkably good state of preservation, but 

 notwithstanding this fact it is a difficult matter to make out 

 the epithelial cells either on the outer surface of the sponge or 

 in the somewhat complicated inhalant canal system. On the 

 other hand, we find in both these situations a very peculiar 

 layer of minute granules, which, when examined under a Zeiss 

 F objective, presents in surface view the appearance shown in 

 fig. 57, and in sections at right angles to the dermal surface 

 the appearance shown in fig. 56. The granules themselves 

 appear slightly elongated and very thickly and evenly scattered 

 over the surface. Embedded in the gelatinous ground sub- 

 stance of the mesoderm, at some little distance beneath the 

 dermal surface, are found numerous very distinct subdermal 

 gland-cells, connected by thread-like processes with the 

 granular layer, as shown in fig. 56. The granules themselves 

 do not stain with borax carmine, and present, under the Zeiss 

 F obj., a very striking resemblance to bacteria. So great 

 is this resemblance that I submitted a fragment of the 

 sponge to Mr. Thomas Cherry, Demonstrator in Pathology in 



