364 HYALONEMA (PHIALONEMA) PATERIFERUM. 



of the specimens allows one to judge, this is also the case in the forms E and F. 

 It is certainly true in some forms, probably in all, that from the margins which 

 mark the boundary between the dermal and the gastral faces there arise centro- 

 tyle amphioxes, diactine pinules, and spicules transitional between these forms. 

 Besides the lateral rays of the pinules, amphidiscs, paratangentially extending 

 centrotyle amphioxes, and the lateral rays of pentactine megascleres are found 

 in the dermal and gastral membranes. According to Wilson {loc. cit.) the amphi- 

 discs of the superficial membranes are large macramphidiscs, and he says that 

 these spicules are very abundant in these membranes of the forms (A and B) 

 studied by him. In the specimens of forms D and E, examined by me, where 

 the superficial membranes are more or less preserved, I found them occupied 

 by micramphidiscs in places very abundant, but nearly destitute of macram- 

 phidiscs. Below the superficial membranes, the apical (proximal rays of the 

 pentactines, centrotyle amphioxes, and a few transitions between them and diac- 

 tine pinules, occur. All these spicules (spicule-rays) are situated radially. 



Hexactine megascleres, canalar pinules, microhexactines, transitions between 

 these and the pinules, and amphidiscs are met in the interior of the body rhabds, 

 which are, for the most part, centrotyle amphioxes. In the vicinity of the point 

 of origin of the stalk stout-rayed acanthophores occur. Many of the rhabds 

 of the interior form bundles which traverse the choanosome. The hexactine 

 megascleres appear to increase in size toward the central part of the sponge. 

 In the forms C, D, E, and F the canalar pinules are scarce, and irregularly 

 and sparsely scattered over the walls of some of the canals only, the walls of 

 other canals appearing to be destitute of these spicules. The microhexactines 

 vary considerably in respect to their size, their spinulation, and the curvature 

 of their rays. Wilson (loc. cit.) considers the large, straight-rayed, and strongly 

 spined ones (in the forms A and B) as canalaria. In the forms D, E, and F 

 these spicules do not appear to be restricted to the canal-walls. In form C I 

 failed to find any of the large, straighter-rayed microhexactines. The hexactine 

 and pentactine transitions between the microhexactines and the pinules are, 

 in the forms D, E, and F true canalaria. The amphidiscs, among which four 

 forms can be distinguished, are exceedingly abundant. Micramphidiscs, chiefly 

 large ones, clothe the walls of the efferent canals of form D in dense masses. 

 In the forms C, D, E, and F macramphidiscs are scattered in very large numbers 

 through the choanosome. According to Wilson (loc. cit.) only few macramphi- 

 discs occur in the interior of forms A and B. The large macramphidiscs are 

 much more numerous than the small ones. The stout-rayed acanthophores 



