VIÏROLLULA FEr.TILTS. 49 



mine whether wo have to do simply witli iiucloi or with cells in- 

 closing each a nucleus, are very small and comjiactly j^acked 

 together. I am ratliei- inclined to view them, as in the case of 

 certain more internally situated elements (arch^eocytes) of similar 

 appearance l)ut of a somewhat larger size, in the light of com- 

 plete cells. The spicules, to which I shall soon return, run for 

 the most part in the peripheral layer just referred to. .Vt the 

 two poles of the larval l)ody, which are apparently destitute of 

 the external epithelium, cellular elements are not recognizalde ; 

 whatever sparse quantity of the ]ii'otO]ilasm exists over and l)e- 

 tween the bundled spicular rays simply appears finely granular. 



The more internal and l^y far the principal part of the 

 inner mass is composed of at least two kinds of cells, viz., those 

 which go to form a reticular kind of tissue and those which 

 retain a more or less spherical shape (fig. 21). The former most 

 likely correspond to the so-called "dermal cells", and the latter 

 to the arclneocytes, known in the inner cellular mass of non- 

 hexactinellidan sponge-larvcT. 



The reticular tissue is most plainly visible in the anterior 

 part of the body, in front of the region where this is broadest 

 (see fig. 21). There it presents a small and open meshed, col)- 

 web-like appearance, consisting of irregularly branching and 

 anastomosing filaments, which are well stained and tolerably 

 sharply defined in contour. The small corpuscles occasionally 

 contained therein, I take for the nuclei. What nature to ascribe 

 to the fluid, which, though imperceptible, undoubtedly fills up 

 the spaces of the meshes, is difficult to directly determine. On 

 the otber hand, I am stroughy inclined to assume that we have 

 in the reticulum an inceptional trabecular system, which, in 

 my opinion (Contrib. I., p. 104), represents at once both the 



