LEIOSELLA. 



123 



subdermal cavity, composed of reticulating, irregular, taugential canals. These 

 subdermal cavities measure on an average 0-14 millim. in width; some of 

 them attain a diameter of 0-6 miUim. The inhalants proper, which arise from 

 the floor of the subdermal cavity, rarely exceed 0-2 miUim. in width. The 

 ciUated chambers are attached to the final ramifications of these canals ; there 

 are no special efferent canals. The small exhalants join to form large canals, 

 which are irregular, sometimes attain a width of 0- 7-0-9 millim., and open 

 into the oscular tubes; the latter are perpendicular to the surface, about 

 1-2 millim. wide, straight, and circular in transverse section. As already men- 

 tioned, the oscula are about 1 millim. wide, so that the tubes appear contracted 



distally. 



The histological structure of this species presents some very striking pecu- 

 liarities. I cannot say to what extent these are due to the exceUence of the 

 material of this species at my disposal, and to what extent to specific pecu- 

 liarities. 



Granular amoeboid wandering ceUs were observed in great abundance in the 

 skin ; these lie under the external epithelium, and also occur in the waUs of 

 the canals leacUng down into the subdermal cavities. Glandular elements are 

 likewise very abundant in the skin ; these are pyriform and filled with large, 

 conspicuous, and highly light-refracting granules. Numerous transition forms 

 between these amceboid and gland-ceUs are observed. In some of the glandular 

 cells, particularly in those which possess very abundant and large granules, no 

 nucl'eus is seen. It appears that the glandular ceUs are entirely converted into 

 the secretion. My sections show that the ripe gland-cells, without nucleus, 

 are expelled in toto from the sponge ; they are often observed passing through 

 the ectodermal epithelium or lying on its outer surface. The cells which are 

 in this way expeUed are replaced by amoeboid wandering cells, and so it appears 

 probable that gland-ceUs may be formed when an emergency occurs, and that 

 they need not necessarily always be present. This may account for the fact 

 that F. E. Schulze and others have failed to observe them. 



The most interesting structures, however, are the highly developed sense- 

 organs, the synocUs. In my original description I stated {he. cU.) that sen- 

 sit'ive spindle-shaped cells had been seen by me. I failed, however, at that 

 time to interpret correctly what I saw. In specimens hardened with osmic 

 acid and stained with picrocarmin,' irregular conic truncate protuberances 

 are observed on the outer surface. These protuberances are broader than high. 

 Below them highly colourable spindle-shaped cells are found in groups of four 

 to eight, disposed in such a manner as to converge towards the low conical 

 process in which they terminate. I do not doubt that this structure is similar 

 to that observed in Calcareous sponges and described by me as a synocil. 

 We find, namely, in hardened specimens of Calcareous sponges very often 



