178 ARTHUR DENDY. 



to possess the typical corticate Syconoid canal system, well 

 shown in Polejaeflf's figure of the anatomy of the sponge. 



Sycyssa. 

 Here, again, the same remarks apply as in the case of the last 

 two genera. The anatomy of Sycyssa Huxleyi is illustrated 

 by Haeckel in his great monograph (5). 



Leucandra (figs. 16, 17, 25). 

 In this genus we meet for the first time with the well-known 

 Leuconoid type of canal system, the essential features of which 

 are shown in fig. 16, representing a portion of a transverse 

 section through the wall of Leucandra phillipensis (4). 

 It will be seen from this figure that the flagellated chambers 

 are small and more or less rounded, and scattered quite irregu- 

 larly but abundantly through the thickness of the sponge wall. 

 Each communicates by several small prosopyles with the 

 irregular inhalant canal system, and by a single larger 

 opening with the exhalant canal system. The gelatinous 

 ground substance of the mesoderm is sparingly developed, 

 except in the region of the dermal and gastral cortex, and 

 the inhalant and exhalant canals are very wide and irre- 

 gular. Numerous small inhalant pores, scattered over the 

 dermal surface, lead first into small canals in the dermal 

 cortex; these unite into much larger ones, which lead inward, 

 and break up in the thickness of the sponge wall. The very 

 wide exhalant canals open into a perfectly well-defined.gastral 

 cavity from which the water passes out through a single ter- 

 minal osculum. 



Such a sponge as Leucandra phillipensis forms a 

 thoroughly typical Leuconoid individual, and we find the type 

 of canal system above described repeated in a large number of 

 species with singularly little variation; the flagellated chambers 

 being irregularly scattered, ovoid or subspherical in shape 

 (fig. 25), and about 0*1 mm. in diameter. 



In a few species of Leucandra, however, we find the flagel- 

 lated chambers much larger, more or less elongated in form, 



