150 



BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



In the transitional pinnules the characteristics of the genital pinnules first 

 appear at the distal end and rapidly extend inward toward the base. 



These intermediate pinnules are followed by from 3 to 35 or more pinnule 

 pairs (usually from 10 to 20) upon which the perfected gonads are developed 

 (figs. 281, 282, p. 215). The firet commonly bears a relatively small gonad, but on 

 the second and following this rapidly increases and soon reaches its full size. 

 After the middle, or the proximal two-thirds, of this pinnule series the gonads com- 

 monly begin gradually to decrease in 

 size, finally disappearing altogether. 



The gonads arise on the third seg- 

 ment and extend outward for a variable 

 distance over from 2 to 20 (usually 

 over from 5 to 10) segments. They 

 are of two distinct types, each of which 

 has a more or less definite range (1) 

 a short abruptly rounded type (figs. 

 281, 282, p. 215) occun-ing in almost 

 all of the species of the Macrophreata, 

 in the majority of the Charitometridae, 

 and in certain of the small 10-armed 

 species of Comasteridse, and (2) a long 

 fusiform type, found in the Tropio- 

 metrida*, most of the Thalassometridse, 

 and in large individuals of large species 

 in certain macrophreate genera. Both 

 types are found in the Heliometrinse, 

 though the second is greatly pre- 

 dominant, and both types are found in 

 Antedon hifda and A. petasus, though 

 only the second in Antedon 'mediter- 

 ranea and A. adriaticn. 



The genital pinnules are, with but 

 few exceptions, shorter than the oral 

 pinnules, and usually very much 

 shorter. The first four or five pairs 

 are of equal, or nearly equal, length; 

 on the following the length slowly and 

 gradually increases, coincident with the decrease in the size of the gonad, until 

 the outer genital pinnules merge imperceptibly into the distal pinnules. The 

 transition from the middle to the distal type of pinnule begins first at the distal 

 end and works gradually inward towai-d the base. 



Ordinarily the genital pinnules (figs. 262-287, pp. 207-215, 302, 303, 307, 310. 

 p. 223; 324, 325, 327-335, p. 227; and 336-311, p. 229) are moderately slender and 

 taper very slowly until near the tip. They are much more nearly uniform through- 



FlG. 210. L.\TEIH 



VIEW OF SPECIME.N 

 METR.\ FLAVA. 



