4 Art. 1. — N. Annandale and T. Kawamura: 



The main element in the skeleton consists of slender but well- 

 defined radiating or vertical fibres composed of spicules connected 

 together by a horny substance. The substance is in continuity 

 with that which forms the delicate membrane at the base of the 

 sponge. The vertical fibres ramify irregularly but not frequently 

 and pursue an irregular upward course. They are joined together 

 to form a loose and irregular network with still more slender and 

 much less well-defined transverse fibres of similar structure. 



Free microscleres are present as well as those associated with 

 the gemmules. The macroscleres or skeleton-spicules are smooth, 

 slender, of relatively large size, sharply pointed at both ends 

 (except in abnormal specimens) and as a rule slightly curved. 

 The free microscleres or flesh-spicules, which are as a rule numer- 

 ous both in the dermal membrane and in the interstices of the 

 skeleton, are similar in form to the skeleton spicules but are much 

 smaller and densely covered with spines.^ The gemmule-spicules 

 resemble the microscleres but are stouter and as a rule more 

 strongly curved; the spines at their extremities are frequently 

 better developed than on other parts, arranged in one or more 

 circles and retroverted. 



The gemmules lie free in the interstices of the skeleton, which 

 does not form special cages or chambers for their protection. They 

 are spherical in form and normally of considerable size, covered 

 with a thick pneumatic coat in which the gemmule-spicules lie 

 tangentially, and with a single micropyle or foramen, which is 

 protected by a cup-like horny structure. As a rule the pneumatic 

 layer is limited externally by a thin horny membrane in which 

 there is a layer of gemmule-spicules lying horizontally. All these 

 accessory structures except the foramen may, however, be absent, 

 and even the gemmule-spicules sometimes disappear. There may 

 be more than one foramen, and the foramina! aperture may take 

 the form of a tube instead of a cup. 



The species is probably cosmopolitan and has been found both 



1) In the European Spongilln rhenana Eetzer, which Weltner regards as a form of S. 

 lacustris, the free microscleres are smooth. 



