114 UlROSttl OHSHIMA 



one of those fifty-lour abnormul larvae also metamorphosed 

 on the same day. Within ten days afterwards 127 normal 

 larvae and six abnormal ones had metamorphosed to young 

 sea-urchins from this culture. Mac Bride (11, p. 2U4) got 

 the larvae of Echinus esculent us to metamorphose in 

 forty-two to fifty days after fertilization, while Allen and 

 Nelson (1, pp. 420-1) found the earhest metamorphosed 

 young of E . a c u t u s forty-two days after fertilization, 

 of E. esculent us, forty-eight to sixty-eight days, and of 

 E . m i 1 i a r i s , thirty-eight days. As compared with these 

 records of regular S(*a-urchins our case was nmch quicker in 

 development. On the other hand, the culture no. 1 1 and others 

 from the same parents suffered from want of food seriously 

 after the first week of their development, and when examined 

 on September B they were, though seventy-six days old, all 

 very far from metamorphosis, the * larval ' body fully developed, 

 but the echinus-rudiment, if present, being very small. The 

 culture no. 0, for some unknown cause, gave poor results. 

 Most of the larvae died off very quickly, and the survivors 

 showed various irregularities in shape. 



The food supply was generally good during the first week 

 or so, but afterwards in most cases it could not be continuous, 

 and became unavoidably very irregular, owing to the unsuccess- 

 ful culture of Nitzschia. 



Now, from among the ' treated ' larvae (nos. 4 and 9), 

 which number 784 in all, there were found 88 inverse (11-2 per 

 cent.) and 6 doubles (0-8 per cent.). In ' controls ' (nos. 1, 6, and 

 11), on the other hand, from among 646 larvae, there appeared 

 69 inverse (10-7 per cent.) and 13 doubles (2 per cent.). This 

 shows clearly that there is no noticeable difference in the 

 rate of producing abnormalities between these two differently 

 treated lots. We shall discuss this question later on (p. 143). 



The results of Professor MacBride's experiments of 

 producing the double hydrocoele (15) may here be cited 

 briefly. 



1914 (pp. 334-5). The larvae three or four days old were 

 treated for ten or eleven days with ' hypertonic ' sea-water 



