Prof. F. Vejdovsky on Freshwater Sponges. 15 



a group of gemmules, even under a low power, it is soon seen 

 that the above-mentioned horn-like tube projects externally 

 from each gemmule. As to the mode in which such groups 

 of gemmules are produced, transverse sections give the most 

 reliable evidence. Thus in a transverse section, showing 

 five gemmules immersed in a common envelope, we see one 

 gemmule placed in the centre of the group, while the other 

 four lie in the periphery of the first. In other sections we may 

 find several more gemmules both at the periphery and in the 

 centre. Every peripheral gemmule projects outwardly by 

 the horn-like tube from the common envelope. The walls of 

 the tube appear much weaker than the thick, dark-brown, 

 horny, proper enveloping membrane of the gemmules, the 

 cellular contents of which contain very numerous elliptical 

 starch-granules. The common envelope of a group of gem- 

 mules consists of hollow indented columns, which appear to 

 be divided into a series of superimposed chamberlets by 

 transverse lamellse. We find here the same arrangement 

 which has already been made known for one series of the 

 freshwater sponges, especially by Carter's writings, and which 

 I have also demonstrated in Trochospongilla erinaceus, and 

 interpreted as an air-chamber layer. It probably represents 

 a modification of the ordinary granular parenchyma-envelope 

 which I have demonstrated in the indigenous species of 

 Euspongilla and Ephydatia, but have also found in the exotic 

 Spongillidse, which I obtained by the kindness of MM. H. J. 

 Carter and E. Potts, namely Tubella pennsylvanica*, Par- 

 mida Batesn, Meyenia Leidyi f, Heteromeyenia argyrosperma, 

 Carterius latitenta and tenosperma, &c. In Meyenia Leidyi 

 and Tubella pennsylvanica the parenchymatous envelope is 

 very deep, so that the amphidisci attached to the horny 

 membrane seem to be quite concealed. The gemmules of 

 Parmula Batesii have the same form as those of species of 

 Ephydatia, namely globular. On the thick horny membrane 

 there stand three alternating series of the scutiform amphi- 

 disci, which appear to be enveloped by a deep parenchymatous 

 layer, as already represented by Carter. 



This parenchymatous layer therefore becomes modified into 



* The form and arrangement of the skeletal spicules of Tubella reticu- 

 lata agree with those represented by Marshall in his Potamolepis Leub- 

 nitzi<e. 



t Meyenia Leidyi certainly contains amphidisci of the same form as 

 Trochospongilla erinaceus, but is by no means identical with the latter. 

 The smooth skeletal spicules and the peculiar form of the depressed flask- 

 shaped gemmules, flattened at the inferior pole, as well as their deep 

 granular parenchyma-layer, are characters which mark Meyenia Leidyi an 

 a distinct species. 



