15 



nized it only in Stelospongtis ßahelliformis and, less plainly, in Hali- 

 chondria panicea\ and, until I know that Dr. von Lendenfeld has 

 carefully examined good sections of well-preserved specimens of the 

 sponge in which I have investigated the question, I must decline to 

 consider his criticism of my work as of any particular value. In the 

 case oi Stelospongus ßahelliformis, moreover, a very little consideration 

 Avill shew that Dr. von Lendenfeld's new explanation of the 

 observed facts is untenable. In that sponge, as I have pointed out in 

 my paper, and as will be perfectly obvious from my figures, the meso- 

 dermal ground-substance exhibits the very distinctly and highly gra- 

 nular appearance characteristic of the group to which it belongs, in 

 contradistinction to the transparent, gelatinous, ground-substance of 

 many other sponges. Here then, if the ground-substance existed in the 

 spaces between the collared cells, as Dr. von Lendenfeld assumes, 

 we should surely have no difficulty in recognizing it by its numerous 

 distinct granules; instead of which the ground-substance terminates 

 perfectly definitely at the level of the nuclei of the collared cells, and 

 so comes to form the floor of a large empty space (the peripheral space) 

 which is roofed over by Sollas's membrane supported on the collared 

 cells. Even supposing that the membrane in question were merely the 

 surface portion of the mesodermal ground-substance, widely separated, 

 in some inexplicable manner, from the deeper parts, it would surely 

 retain traces of its granular nature , but , unfortunately for Dr. von 

 Lendenfeld's hypothesis, it does not; it is characteristically hyaline 

 and transparent, and is in all probability simply a special development 

 of the collars of the collared cells, and hence endodermal, and not 

 mesodermal in origin (compare also Sollas, article »Sponges«, En- 

 cyclopaedia Britannica). 



Concerning my figures Dr. von Lendenfeld observes »Es ist 

 jedoch seine schematische Darstellung dieser Membran (Taf. 32 Fig. 9) 

 keineswegs Vertrauen-einflößend, sondern eher ein Beweis der theo- 

 retischen UnWahrscheinlichkeit der Existenz derselben«. He forgets, 

 however, to mention that I also give two figures (Figs. 7 and 8) plainly 

 shewing the membrane, which are not diagrammatic in the slightest 

 degree ; they are as exact representations of actual preparations as I was 

 able to produce, while Figure 9 is simply intended for a diagram and 

 described as such. So distinct is the membrane in question that I have 

 been in the habit of demonstrating it to students at the Melbourne 

 University, who have sketched it from nature perfectly distinctly in 

 their note books; Professor W. Baldwin Spencer, also, permits me to 

 say that he has examined my preparations and is satisfied as to the ac- 

 curacy of my drawings and description. 



