

i 



56 



THE SPONGES. 



long; 



centrum with a 



ray is about 45 /x long ; terminals about 60 /x 

 diameter of 20 /x. 



That the oetaster rays are secondarily produced, as Schulze (1893) has 

 demonstrated, by the fusion of components, which themselves are derived 

 from the rays of an original hexact, is well shown both in the typical 

 and "abnormal" spicules of this species. The various facts described by 

 Schulze (I. c.\ such as the trilobed transverse section of the oetaster rays, 

 the ridges passing from the central protuberances out upon the rays, and 

 the delicate row of lacunae, extending lengthwise through the latter, may 

 all be observed in the typical spicules. The axial cross is plainly visible 

 in the centrum, as Ijima (1897, p. 44) pointed out. It frequently happens 

 that, as in some of the species described by Schulze, e. g. Rliabdocalyptns 

 mirabilis (Schulze, 1899, Taf. XIII.), one or several accessory rays which end 

 like the terminals are developed as outgrowths from the central protuber- 

 ances (Fig. 8, Plate 6). It also happens not infrequently that the fusion 

 of the originally separate components is very incomplete, in which case 

 the oetaster ray appears split to its very base, as in one of the rays of 

 Fig. 10, Plate 6. In some cases there is almost no fusion, as in some 

 of the rays of Fig. 4, Plate 6. Where the fusion is imperfect, and in 

 addition several of the protuberances on the centrum are directly pro- 

 longed into rays, a very irregular spicule is the outcome, in which the 

 oetaster character is not conspicuous (Fig. 4, Plate 6). Irregular spic- 

 ules of this kind are referred to by Schulze in several places (1887, 

 p. 157 ; 1893, p. 6). 



Oxyhexasters are abundant in the parenchyma. The principal rays 

 are smooth, cylindrical, about 3 /x long. There are two terminals to each 

 principal, nearly straight, strongly diverging, slender, and tapering evenly 

 to the point, about 35 /x long. Oxyhexasters are common in which on 

 one or more of the principal rays only one terminal is present. The 

 remaining terminal and the principal ray may or may not make an angle 



with each other. In the latter case the division point between principal 

 and terminal is not recognizable. When all six rays are of this character, 

 a small hexact is produced such as has been designated by Ijima (1897, 



p. 45) a hezactin-shaped oxyhexaster : 

 looked for, but none were found. 



Microdiscohexasters were carefully 







* * 







