44(> 



THE VOYACK OF H.M.S. CHALLENGER. 



or throughout the whole body, as in Kuplcctdla aspergiilwm, in its mature condition. I 

 can, therefore, regard neither the union of spicules into a continuous trabecular skeleton, nor 



that particular mode of their union by means of the 

 opposition of the corresponding branches of spicules 

 and covering with a common envelope, as a sufficiently 

 constant character for the diagnosis of the Dictyonina, 

 and for the division of the Hexactinellida into two 

 primary classes, although I do not wish to deny that 

 there are certain differences in the mode of union of 

 the rays of the spicules between the Dictyonina on 

 the one hand, and the Lyssacina, which are provided 

 with a firmly united skeleton, on the other. 



"On the contrary I find the chief difference between 

 the above mentioned divisions of the Hexactinellida 

 to be this — that in the Dictyonina the skeleton is already deposited during the formation 

 and growth of all the parts of the body, and hence typically and necessarily by the 



J^'ig. lt>». — Myliusia callocyatkus, Gray, 

 a representative of the Inermia. 



JT 





Fig. 169.— Characteristic forms of the dermal spicules of the four families of Lyssacina. 

 o, dagger-shaped spicule of Waltcria fiemmingii, n. gen. et sp. (a Buplectellid) ; b, " Pinulus," fir-tree shaped spicule of 

 Sympagella nux, 0. Sch. (an Asconematid) ; c, "Pinulus," and d, "Amphidisk" of the external surface of Ilyalonema 

 sieboldi, Gray (a Hyalonematid) ;. t,f, g, dermal spicules of Hossella antarctica, Carter (a Rossellid). 



union of certain spicules in more or less regular arrangement, whilst in the Lyssacina 

 either a continuous trabecular skeleton is entirely wanting or only formed at a later stage, 

 partly by the enclosing of irregularly disposed spicules at their points of crossing or of 



