192 



DlGTYOSPONGID.fi. 



FiGUnE 41. Spicules of Physospongia Dawsoni, X400. 

 Fragments of eohinate hexacts, a smooth-rayed peutact, 

 a diact and part of a c'leme. (J. M. C.) 



(loc. cit. fig. 1). The separation is of such a nature that only the cylindrical 

 rods adhere to the gastral cast while the anchorate spicules and denies 

 are beautifully displayed in their original position upon the enveloping 



matrix. The secondary vertical lateralia 

 and the horizontal reticulating bands are 

 composed of comparatively few cylindrical 

 spicules, some of which attain a greater 

 size than any observed in the jjrincipal 

 lateralia, but neither of these series has 

 shown any trace either of the anchorate or 

 of the clemate spicules. 



Mention has been made of the radiate 

 tufts produced by the extension of the 

 horizontal spicular rods at their intersec- 

 tion with the vertical latei-alia of both 

 series. The spicules of the horizontal 

 lateralia ap[)ear to lie nearer the gastral 

 surface than do the principal and secondary vertical bundles. At the intersec- 

 tion of the horizontal and vertical bundles are occasionally seen large pentacts, 

 sending a ray along eaeh bundle departing from that point, the fifth ray 

 passing inward. These pentacts are the heaviest parts of the skeleton, and 



as they lie abt)ve or outside of 

 the lateralia they probably belong 

 to the dermal surface. 



The dennal surface of the 

 quadrilles formed by the intei-sec- 

 tion of the lateralia is regularly and 

 very finely reticulated by smooth- 

 rayed pentacts lying in apposi- 

 tion. These vary in size but are 



Figure 42. Physospongia Dawstmi. A somewhat diagrammatic fig- .| i_ lI ^ 



ure of one of thcspicuiar tufts, xio. (J. M. c.) ncver iiiorc than ouc- tenth as large 



as the smooth pentacts at the intersection of the lateralia. Among the spicules 

 \vhich evidently belong to the parenchyma of the sponge are numerous frag- 

 ments of echinate branches, some of which undoubtedly are parts of echinate 

 hexacts, as that represented in figure 41. The same figure shows a fragment 

 of a large spicule in which the surface sj)inules are more produced than in any 

 of the echinate spicules of other species. This form of spicule seems to be of 

 rare occun-ence in the species, and from analogy with jP, Colletti, Cleodlctya 





