CHAUNOPLECTELLA CAVERNOSA. 63 



The paratangeiitials are nearly straight; sometimes they are seen 

 to exhibit an uneven surface throughout their entire length, due 

 to the presence of obsolete warty prominences. Tlius, in its 

 composition and in the arrangement of the elements, the dermal 

 layer is here essentially the same as I know it in Leucopsacus or 

 in Ghaunoplectella spinifera. 



But a very remarkable difference in the spicular composition 

 of the dermal Inyer is presented by large individuals. With the 

 growth of the sponge, it seems the dermalia are constantly 

 supplemented by spicules genetically belonging to parts directly 

 underlying the dermal membrane. In other words, a large number 

 of peripherally situated parenchymalia are apparently taken up, 

 as it were, into the constituency of the dermal skeleton. The 

 process seems to l)e not without analogy in other Hexactinellids. 

 Thus, in some Euj)lectellids certain hexactinic spicules, which 

 have taken their origin right among the parenchymalia, show 

 indications of being shifted on to the surface, to be taken into 

 the rank of the dermalia (Contrib. I., pp. 47, 74, 235) ; further, 

 the so-called liypodermalia are in all cases spicules which are 

 apparently most nearly related to parenchymalia but have gone 

 by adaptation into the support of the dermal layer. But it must 

 not be supposed from this that certain spicules in the dermal 

 skeleton of mature Ckaunopleclella caveimosa are to be regarded 

 as liypodermalia and the rest, as dermalia proper. The fact is, 

 at any rate, that none of the dermalia in any stage of the sponge's 

 growth can be distinguished as liypodermalia, a point common to 

 all the Leucopsacids as well as to the Euplectellids in general. 



In surface-view preparations of the dermal layer taken from 

 large specimens (PL lY., fig. 7), tlie spiculation resembles in a 

 measure the parenchymalia as seen in choanosomal septa. This 



