476 



Mr. Gr. Bidder. 



[May 12, 



suggestive of the hypothesis that they are loci of discharge, first 

 into the gastral cavity, subsequently on the exterior surface. To 

 this they have obviously pushed their way (cf. fig. 2), possibly in 



FlQ-. 2. — Section through the wall of Ascetta clathrus. Osmic acid. Nuclei not 



stained. 



consequence of the occlusion of the gastral cavity. For the flask- 

 shaped ectoderm cells, their whole form and disposition indicate with 

 certainty that they are glands discharging to the exterior. 



A completely different set of granules, which must not be confused 

 with these, are found in the normal collar cells of many sponges ; for 

 distinction it may be well to speak of them as " basal spherules of 

 the endoderm," or simply "spherules." I have mainly experimented 

 on them in Sycon raphanus, Ascaltis cerebrum, and Ascetta primordialis 

 (so-called). In the fawn-coloured varieties of these two latter species, 

 the basal spherules give the colour to the sponge; in the living 

 8. raphanus they are of a greenish tint, more refractive than the 

 protoplasm, but not highly so.* They never blacken with osmic 

 acid, nor give a port wine reaction with iodine, nor do they show 

 any coloration in a sponge which is excreting indigo (A. primordialis). 



In the fresh condition they stain (S. raphanus) more deeply than 

 the nucleus with acetic acid and methyl-green, and with osmic acid 

 and methyl-green, but they are not stained red by picrocarmine after 

 osmic acid. In permanent preparations they appear with osmic acid 



* Similar greenish granules were observed in Spongilla by Lieberkiihn in 1856 

 and Carter in 1857. Saville Kent ('Manual of Infusoria,' p. 80) considers the 

 colour to represent " the predominating refractive index of abnormally minute pro- 

 toplasmic bodies" on grounds which at least point to its frequent occurrence. 

 Similarly disposed granules, but of pint, violet, or other colour, have been frequently 

 observed in the collar cells of sponges. 



