538 E. A. MINOHIN. 



layers, the youngest part, is [sic] harder, and resists the action 

 of reagents ; the whole spicule is composed of prisms formed 

 as cuticular productions by the cells clothing the spicule 

 from without '' (p. 980). "The spicules first make their 

 appearance within cells, and the axial rod ("not canal !) is part 

 thereof. The succeeding layers are cuticular productions of 

 endothel cells." The author gives no pictorial illustrations 

 of his researches on spicule structures, but he has a figure 

 showing '' mesoderm cells ^^ forming an "endothel" " in the 

 the shape of a hollow tube " covering the rays of a triactine 

 of "Ascetta procumbens^' (1885 [1], pi. Ixiii, fig. 3; and 

 description, p. 1146; also [2], p. 980). He is more successful 

 in his delineations of hard structures than of soft, since he 

 draws quite correctly the sharply conical form of the rays of 

 the young triradiate as compared with their more cylindrical 

 contour when fully formed. 



Lendenfeld's later statements with regard to calcareous 

 spicules are not much happier than his early efforts in this 

 direction, and a few quotations may serve to make clear 

 his standpoint. On p. 198 of his work on Adriatic sponges 

 (1891) we read, "On the surface of the spicules [of Clath- 

 rina primordial! s] one observes not infrequently flattened 

 cells, sometimes provided with processes, which singly or 

 united in small groups partly envelop the spicule." In 

 opposition to Metschnikoff the author finds that " the irregu- 

 larly shaped lumps of protoplasm " which envelop young 

 spicules, or are applied to them, are fairly transparent and free 

 from refractile granules (p. 199). " The spicules probably 

 arise in cells, but it must be pointed out that even the 

 youngest of the large spicules which are to be found in the 

 sponge body are much longer than any known sponge cell 

 with exception of the ripe ova. The further growth of the 

 spicule takes place by means of numerous cells, which settle 

 on the surface of the young spicule and precipitate spicular 



substance upon it The skeleton-forming elements are 



always cells of the intermediate layer (Zwischenschicht) " 

 (p. 383). These three sentences furnish a good instance of 



