OCULAR AND GKNITAI. IM.ATKS. 



107 



smooth and 10 has the primary tubercle. In the adult (text-fig. 94), plates 14 to Hi are -month 

 and 13 has the primary tubercle. This is in accordance with what I -howed '.lack-on. 1899) 

 as localized stages in development in Strongyloccntrotiis and Arlaeia. that the young hurt, 

 added plates are simple, and that differential characters are progressively added > the platrx 

 grow older and are pushed ventrally by newly added plates on their dorsal border. 



It would be extremely interesting to study a large series of young developing Crntrrchinut 

 setosus. I succeeded in getting 110 specimens from 8 to 40 mm. in diameter from the \\V-t 

 Indies, Bermuda, and the Pacific. Of this series, as shown in the table (p. 155), 23% have 

 all oculars exsert, 5 % have I insert, 9 % I and V, and 55 % have the adult typical char: 

 of I, V, IV insert. Progressive variants in this immature series are infrequent, as would In- 

 expected; 5% have I, V, IV, II insert, and 3% have all oculars insert. With later growth 

 unquestionably more oculars would have come in in some of the specimens, so as to give tin- 

 usual adult percentage of progressive variants. There are two aberrant variants, one with 

 oculars V, IV, and one with I, V, IV, III insert. 



m 



* 



nr 



95 



93 



1 



TEXT-FIGS. 93-95 Ocular plate arrangement in Centrechinus seloswi (Leske). 



93 Bermuda. Diam. 85 mm. R. T. J. Coll., 686. X 2.5. Oculars I, V, IV inw-rt. tl 



94. Florida. Diam. 70 mm. 11. T. J. Coll., 687. X 2.5. Oculars I, V, IV, II insert, progrc 

 cral plates simple dorsally above the 24th, which is the first compound plain (pp. 56, 174) 



95. Florida. Diam. 82 mm. R. T. J. Coll., 688. X 2.5. All oculars insert, a progrc 



The development of ocular plates of Centrechinus being as above descried, the adult 

 shows striking features as a matter of individual variation. All individuals considered under 

 variation were not fully grown, any more than in other species, but all here considered are 



