DESCRIPTION OF EPHYDATIA BLEMBINGIA. 79 



acids. It often happens, that, in sections, it splits in two, a 

 result broug'ht about by the weakening produced through the 

 inner ends of the amphidiscs being embedded in it, and not 

 lying upon it as is usually described in the gemmules of 

 Ephydatia. The line along which the splitting takes place 

 is that in which the discs are situated (PI. 4, fig. 17, a). 



The middle layer of the gemmule coat is by far the thickest 

 and approximately extends over the whole length of the shafts 

 of the amphidiscs. It is clear in structure, and presents in 

 section the appearance of ordinary parenchyma with very 

 small granules at the nodes. In the fully developed gemmule 

 there are no lines of division indicative of the different cells 

 out of which it was originally formed (PI. 4, fig. 17, a). 



The outer layer of the gemmule coat is thinner than either 

 of the other two, and in it are embedded the outer ends of 

 the amphidiscs. It consists of the same substance as the 

 inner layer but is much more granular. In the mature gem- 

 mule it is often rubbed off, and consequently the outer discs 

 of the spicules protrude from the gemmule coat (PI. 4, fig. 

 17, a). 



The amphidiscs lie partly in the three layers. The inner 

 disc lies in the corresponding layer, the shaft in the middle 

 layer, and the outer disc in the thin outer layer. They are 

 so closely packed that the discs overlap one another and 

 consequently are not on the same level. Their shafts never 

 seem to cross one another, but lie approximately parallel. 



III. The Affinities of Ephydatia blembingia. 



The presence of gemmules in the material at my disposal 

 made the task of determining the systematic position of the 

 fresh-water sponge here described a comparatively easy one. 

 The possession of gemmules excludes it from the sub-family 

 Lubomirskinae, which is a sub-family created for the pur- 

 pose of grouping together a number of fresh-water sponges 

 in which the gemmule, if it does exist, has not yet been 

 discovered. Further, the existence of the thick coat which 

 surrounds the gemmule cells and which contains, embedded 



