io6 Papers from the Marine Biological Laboratory at Tortugas. 



In two particulars the Amphipholis from Montego Bay showed rather 

 striking differences from those studied at Newport by Fewkes (1887), who 

 says that 4- and 6-armed young "were repeatedly found" and that "adults 

 with 6 arms were common." I have not found a specimen in my Jamaican 

 material, either adult or young, which varies in any way from the typical 

 pentamerous condition. Again, Fewkes says that "ordinarily a gravid adult 

 would have from 10 to 15 (generally 10) free young," In the Jamaican 

 form the number of young ranged from i to 3, but in no case were more 

 than 3 seen. There were no 2 of the 3 at the same stage of development; 

 for example, in one typical case one young was 0.50 mm. across with 5- 

 jointed arms, a second was 0.63 mm. across with 8-jointed arms, and a third 

 was 0.80 mm. across with ii-jointed arms. The young are not born until 

 the disk is nearly a millimeter across; one mother only 2.2 mm. across the 

 disk contained a young one 0.90 mm. across. Fewkes does not mention the 

 size of his adults, and it is quite possible that they were much larger than 

 the Montego Bay specimens. If so, that fact might account for the physi- 

 ological differences just noted, in the frequency of variation, and the number 

 of young. Or it is possible that the small number of young may have been 

 due to the breeding-season being nearly over at Montego Bay. No special 

 attempt was made to settle the matter, as it was not until after my return 

 to Cambridge that I had any doubts as to the breeding-season being at its 

 height. 



Unlike Ophiactis, Amphipholis shows no evidence of schizogonous repro- 

 duction, but ordinary reproduction by ova begins very early in life. The 

 development has been so carefully worked out by Fewkes (1887) and Lud- 

 wig (1881), as well as by several other students, that there is little that is 

 new for me to set forth, except in certain details omitted by these earlier 

 writers. As in the case of Ophiactis, attention has been centered on the 

 skeletal parts, as neither the podia nor any other soft parts reveal any 

 features of interest, from the present point of view. 



DISK-COVERING. 



In the youngest specimens seen the disk was covered by 16 plates (a 

 central, 5 large radials, and 10 interradials) as figured by Ludwig, but the 

 5 pairs of radial shields were already beginning to appear. By the time 

 the disk is 0.80 mm. across, there are 5 more radials and 5 more interradials, 

 while the radial shields are now easily recognized as such. The new radial 

 and interradial plates arise between the central and the primary plates of 

 radii and interradii. With increasing size of disk the conspicuousness of the 

 primary plates disappears, and while they can sometimes be made out in 

 the adult, they are not as a rule easily seen. The adult disk is covered 

 by 150 to 300 plates. No spinelets develop in connection with any disk- 

 scales. 



