Dr. A. Wierzejski on Freshwater Sponges. 301 



The nuclear vesicle lying at the surface does not acquire the 

 characteristic iodine-coloration. Jud2:in2: from this reaction 

 with iodide of potassium we might suppose the presence of 

 glycogen in the vesicular cells. But as when the preparations 

 treated with Lugol's solution are heated the colour does not 

 disappear, and the material in question appears to be insoluble 

 in water, we must reserve the tinal decision until it has been 

 converted into sugar. A test for amyloid gave negative 

 results, as also for sugar. 



Although the nature of the substance contained in the 

 vesicular cells remains for the present unknown, their be- 

 haviour with iodide of potassium furnishes us with a means 

 of at once recognizing Meyenia Midler i^ even in small frag- 

 ments, by the characteristic coloration of the vesicular cells. 

 The circumstance that the vesicular cells occur at all periods 

 of the life of the sponge, and even take part in the develop- 

 ment of the gemmules, and, further, that in the regeneration 

 of the stock from the gemmules they appear immediately after 

 the emergence of the contents, indicates distinctly that they 

 have a not unimportant part to play. It may b? that they 

 store up reserve material, or that they furnish nutriment to 

 the cells surrounding them, or produce a secretion of some 

 kind ; at any rate, however, they indicate a peculiar oeconomy 

 in Meyenia Miilleri, distinguishing it from all other species. 



After this brief description of the histological peculiarities 

 of this species I need hardly add that it ought to have a special 

 ])osition in the system of the freshwater sponges. Further, I 

 would point out that by the generally triple arrangement of 

 the amphidisci in the shell of the gemmules, by the extremely 

 rare development of the sexual products, and finally by the 

 usually tuberculate skeleton-spicules, it seems to be sufficiently 

 separated from the other Meyeninte. 



I have still to make a brief remark upon the following state- 

 ment of Dr. Vejdovsky. This naturalist states (Zool. Anz. 

 no. 239) that he induced M. Petr to investigate the minute 

 structure of the external envelope of the gemmules of various 

 Spongillidie, and that the latter had succeeded in demon- 

 strating " that this envelope in most species shows the same 

 structure that occurs mucli more distinctly in S.fragilis, S. 

 nitenSj and Trodiospomjilla erinaceus.'''' 



This result of M. Petr's I must characterize as perfectly 

 correct, especially as, in my memoir published in 1884 {loo. 

 cit. p. 27), the following passage occurs in the concluding 

 remarks : — " The remarkable coating of the gemmules of Sp. 

 fragilis [Lordii) and Trochosjjongilla erinaceus represents 

 o-enetically the insignificant reticulation between the amphi- 



