144 Papers from the Marine Biological Laboratory at Tortugas. 



In the next larger series, 25 to 30 mm. diameter (240 specimens), 21 per 

 cent have all oculars exsert; 3 per cent have ocular I, and 8 per cent have 

 ocular V alone insert ; 14 per cent have oculars I, V, and 45 per cent have 

 oculars, I, V, IV insert. As this last is the species character, it is of note 

 that this is the first stage at which this species feature has become a dominant 

 character. In i per cent, oculars I, V, IV, II, and in i percent all oculars 

 are insert. Seventeen specimens, or 7 per cent, have an aberrant arrange- 

 ment. Of these, 4 have ocular IV only insert; 11 have oculars V, IV, one 

 has I, V, II, and one has oculars I, V, IV, III insert. The occurrence of 

 I, V, II insert as an aberrant variant is of interest because this, as previously 

 shown, is a common aberrant when three oculars reach the periproct in the 

 Echinidse and Strongylocentrotidae, and occurs also in the Stomopneustidse. 



1 have not found a case of I, V, II insert in the Cidaridaj, and it is the only 

 case seen in Centr echinus setosus, although in this species, 1,398 cases of 

 I, V, IV insert have been observed. 



In the next series of Centrechinus setosus, 30 to 35 mm. diameter, 245 

 specimens, 10 per cent have all oculars exsert; 2 per cent have I only; 

 and 12 percent have V only insert; 5 per cent have I, V, and 63 per cent have 

 I, V, IV insert; 4 per cent have I, V, IV, II insert. Of aberrants, there are 

 4 per cent, these consisting of 8 specimens with oculars V, IV insert, and 



2 with oculars I, V, IV, III insert. 



The next series, measuring 35 to 40 mm. in diameter, 169 specimens, 

 has 5 per cent with all oculars exsert; 2 per cent with I only; and 3 per cent 

 with V only insert; 5 per cent have I, V, and 71 per cent have I, V, IV insert; 

 6 per cent have I , V, IV, 1 1 , and 2 per cent have all oculars insert. Aberrants 

 are 5 per cent; of these, two specimens have ocular IV alone insert; i has 

 I, IV; 4 have V, IV; and 2 have I, V, IV, III insert. 



The series 40 to 50 mm. in diameter is considered the last of the devel- 

 oping series. Of this size, 162 specimens, 4 per cent have all oculars exsert, 

 I per cent have ocular I, and 0.6 percent have ocular V only insert; 6 per 

 cent have oculars I, V, and 70 per cent I, V, IV insert; 9 per cent have 

 oculars I, V, IV, II, and 6 per cent have all oculars insert. Of aberrants 

 there are 3 per cent, one specimen having V, IV and 4 having I, V, IV, III 

 insert. The series 35 to 40 mm. and 40 to 50 mm. in diameter make a close 

 approach to the mature series as regards the species character of I, V, IV 

 insert, but these two younger series have more of the developing and fewer 

 of the progressive characters than are seen in the older series. 



While Centrechinus setosus is profusely abundant at Montego Bay, 

 specimens do not attain as large a size as in Florida, from which locality 

 many individuals exceed 100 mm. in size. Of the adult series from Montego 

 Bay, 50 to 80 mm. in diameter, 162 specimens, one specimen, or 0.6 per cent, 

 had ocular V only, and one had oculars I, V insert, both of these specimens 

 are between 50 and 60 mm. in diameter; 73 per cent have I, V, IV insert, 

 the species character; 13 per cent are progressive variants with I, V, IV, II 

 insert and 10 per cent are extreme progressive variants with all oculars 



