MATERIALS FOR A MONOGRAPH OF THE ASCONS. 541 



he termed the porocytes. Even in zoology truth is sometimes 

 stranger, or seems so, than fiction. 



In 1895 I published a preliminary account of the origin of 

 the triradiate systems of Clathrina coriacea, and in 1896 

 I sliowed that the monaxon spicules in the young Leu co- 

 sole nia variabilis are formed each by a cell of the flat 

 epithelium. The last author who has written upon calcareous 

 spicules is Doderlein in the present year. In Petrostoma 

 Schulzei the author finds young quadriradiates in the cortex. 

 " From them ... by reduction (Verkummerung) of one of 

 the four arms arises the triradiate. This derivation of the 

 triradiate calcareous spicule seems to me much more natural 

 than the opposite view " (p. 21). The author does not clearly 

 state what he means by " the opposite view," and his remarks 

 might at first sight be supposed to refer either to Haeckel or 

 to my theory, published two years before (1895) ; but as he 

 makes no mention of my preliminary note on the origin of the 

 triradiate systems, the author's words must be supposed to 

 have a more abstract reference, and to be intended simply as 

 an exposition in general terms of his views on the phylogeny 

 of calcareous sponge spicules. 



Since Doderlein was only able to study dried specimens of 

 Petrostoma, we learn nothing from his description as to the 

 relation of the young spicules to the soft parts. 



To sum up the results of our researches in the literature of 

 calcareous spicules : we might divide the authorities in this 

 field conveniently into two classes or groups, of which the 

 first would comprise Kolliker, Lieberkiihn, and Metschnikofi"; 

 the second all the remaining authors. From the former we 

 obtain valuable observations, but no theories ; the latter give 

 us, on the one hand, plenty of theories, which would be valuable 

 if they had any foundation of fact ; but of observations, on the 

 other hand, next to nothing. Until the publication of 

 Metschnikoff's work (1879) the predominant authorities were 

 in favour of an origin for the calcareous spicules in the gela- 

 tinous ground substance of the body- wall. Metschnikoff having 

 destroyed this notion by demonstrating a cellular origin for 



