J30 BULLETLN 82, UNITED STATES NATIONAL MUSEUM VOLUME 1 



the sixth segment; these are followed by one on the proximal side bejond which is a 

 simple pinnule tip. The ambulacrnl furrow is well developed throughout the whole 

 length of this phuiule. 



In a thu-d specimen, P3 on the posterior arm of the left anterior ray has in the 

 proxijnal portion the character of a true genital pinnule, but beyond the eighth segment 

 regularly alteriiatiiig pinnules are developed as in a true arm, the segments of the main 

 pinimle assuming a much more robust character than normal pinnulars, though they 

 are not so robust as brachials. The fifteenth and sixteenth segments form a syzygial 

 pair, and there is another syzygial pair after an interval of two muscular articulations. 

 There are 6 pinnules on either side, all except the last on the distal side having the 

 gonad highly developed. After the sixth pinnule the mam axis continues and ends as 

 a typical pinnule. 



In a fourth spcchncn, P3 on the anterior arm of the right anterior ray has developed 

 into an arm. The four proximal segments have the character of true pinnulars, though 

 they are somewhat more robust than usual. From the fifth segment regularly al- 

 ternating pinnules are developed and the segments of the main axis assume the charac- 

 ter of true brachials, the tenth and eleventh forming a syzj'gial pair. The tip of the 

 arm is broken off. The portion preserved bears four pinnules on either side, all of 

 which have the character of genital pinnules. The basal portion of the main pinnule 

 does not carry a gonad as was the case in the preceding. 



Mortensen points out that in the arms developed from the oral pinnules no genital 

 organs are found, while in those developed from the genital pinnules all the pinnules, 

 including the lowest, have these well developed. This is in accordance with the struc- 

 tural diiference between oral and genital pinnules, the former not receiving a branch 

 from tlie genital rhachis while possessing a water vessel so that in them the water vas- 

 cular apparatus maj"^ become completely developed. 



With forked pinnules: In one specimen, Pi on each arm of the right anterior ray 

 is forked. That on the anterior arm divides on the fourth, that on the posterior arm 

 on the fifth segment. In both, the two derivatives are equally developed and retain 

 their characteristic structure throughout. 



Dr. T. Gislen (1924) has also described some abnormal specimens. In one of 

 these, P, on one arm was developed like an arm with pinnulars 8 to 11 themselves 

 bearing pinnules. A second specimen showed a similar abnormality and at the same 

 time had another P, forked. A 6-rayed Xll-armed specunen had a forked P3 with 

 a reduced gonad. 



Early stages. — Dr. Th. Mortensen (1920) has given an account of the early stages 

 of tiiis species. 



The fertilized eggs and young embryos are not attached to the pinnules as in the 

 other species of the genus, but drop at once from the pinnules and fall to the bottom. 



The fertilization membrane is covered with short spines, almost as in a Callionymus 

 egg, and is very different from the nearly smooth membrane of the other species. Oc- 

 casionally he saw the eggs floating and suggests that in nature the eggs do not he on the 

 bottom, the spinous membrane serving as a floating apparatus. 



The eggs are about 0.15 nnn. in diameter, yellowish red and opaque. The cleavage 

 is total and regular. After about 20 hours the embryo bcguis to rotate within the egg 

 meml)rane and soon afterwards, generally at about 24 hours, the embryo becomes free 



