REPORT ON THE HEXACTINELLIDA. 89 



penetrated into the Sponge parenchyma, and on the surface of Sponges which are set in 

 cavities of stones or are surrounded by sand and graveh 



Several attempts have been made to utilise for systematic purposes the various modes 

 in which the spicules are more or less united into a framework. Thus, in contrast to 

 the Coralliospongia, which possess a firmly united spicular framework, Saville Kent has 

 named the HexactineUida in which spicules remain disconnected, Calicispongia, and 

 Carter has distinguished the following three great groups: — (l) spicules united ])y 

 silicified fibre ; (2) spicules united by amorphous sarcode ; (3) spicules united partly by 

 vitrified fibre, and partly by amorphous sarcode. 



Marshall, on the other hand, maintains that the free or united condition of the 

 spicules is less significant in the classification of HexactineUida than the manner in 

 which the union actually occurs. His distinction of Synauloidse, with open communica. 

 tion between the axial canals of all dictyoualia, and Asyuauloida^, without such a union 

 of the axial canals, did not, however, find acceptance, for it was soon shown that there 

 are no Synauloidse in this sense. Zittel accepted Marshall's ideas, however, to this 

 extent, that he also based his classification mainly on the nature of the union between 

 the dictyonalia, and distinguished two great divisions, Lyssacina and Dictyonina. 

 The Lyssacina of Zittel embrace, besides forms with disconnected spicules, those in 

 which there is simply a cementing of the spicules, that is to say, such an external 

 union that the spicules do not seem to be checked either in their free arrangement 

 or in their perfect development. In the Dictyonina the spicules of the lattice- 

 framework, the dictyonalia, are, on the other hand, normally fused in such a way that 

 the corresponding rays of neighbouring spicules are closely apposed, and become so 

 completely united by a uniform coating of silex, that their original independence is 

 revealed only in the presence of two separate but closely approximated axial canals. 

 Zittel has also drawn attention to the fact, that Dictyonina frequently possess spicules 

 which are apposed and bound together in more ii-regular ways ; and 0. Schmidt has 

 confidently maintained the occurrence of transitional forms between Lyssacina and 

 Dictyonina. He insists that this dictyonal character is manifested by many forms, 

 as, e.g., in his genus Hertwigia, in the firmly united inferior portion, while the loose and 

 irregular union of the spicules in the middle, and the entire absence of fusion in upper 

 and outer portions, relates the form to the Lyssacina. 



It seems to me indeed diificult to distinguish, in many cases, whether a form belongs 

 to the Lyssacina or Dictyonina. I have, in fact, found forms in which, in a few places, 

 regular fusion was to be observed, while, in other respects, almost all the spicules were 

 cemented together in the irregular way of the Dictyonina. I have, therefore, long 

 endeavoured to find other characters which might serve as sure points of distinction 

 between the two groups, but I have been able to discover only one fact, which might, 

 indeed, justify a separation of the groups, though only at best a distinction of degree, 



