316 A MONOGRAPH OF THE AUSTRALIAN SPONGES, 



(Plate XXXIY., fig. 23, T), which projects beyond the surface to 

 some distance. (1) 



The protoplasm of these cells is very intransparent, and shows 

 after treatment with osmic acid the large dark granules peculiar 

 to the sensitive protoplasm of Hydromedusje after treatment with 

 the same re-agent. The nucleus is large, elongate and oval. 



Below, these cells taper or widen and seem to send forth threads 

 of Protoplasm which pervade the ground-substance. 



These threads are very indistinct and only rendered visible by 

 the large black granules imbedded in them after treatment with 

 Osmic acid. 



Below these groups of sensitive cells, we find large, and beauti- 

 fully developed multipolar Ganglia cells, with numerous much 

 ramified processes on all sides, a dark granular protoplasm and a 

 spherical nucleus in the centre. 



These elements measure 0-01 mm. across ; the nucleiis has a 

 diameter of 0005 mm. This nucleus appears nearly black after 

 treatment with osmic acid and picric acid carmin. (Plate 

 XXXIY., figs. 23, ^.) 



A direct communication between the basal centripetal processes 

 of the sensitive cells and the ramifications of the nerves which 

 originate from the ganglia cells has not been observed by me with 

 suflficient clearness. I think that the figure represents well what 

 I have seen ; even with the homogeneous immersion the doubts 

 could not be removed on this score, but / believe that such a con- 

 nection does exist. 



(1) The nervous elements can be seen in alcohol-carmin specimens, but 

 they are much better visible in specimens treated with Osmic acid and 

 stained with Picric acid carmin. It is necessary to make very fine sections 

 to demonstrate these elements. The length of the Palpocil cannot be 

 ascertained, because it naturally shrinks under the influence of Osmic acid. 

 In the best sections I have, it projects beyond the surface about 6'002 mm. 

 I believe, however, that it must be much longer in life. I have taken great 

 pains to see these structures in the living state, and have drawn the palpocils 

 according to what I believe to have seen. Anyone acquainted with the 

 study of sponge liistology will admit the great difficulty in the way of such 

 oV)servations, and will value the correctness of the result accordingly. This 

 of course only relates to the lem/th of the pelpocil, its ]rjrt>>ence cannot be 

 doubted. 



