98 lr. II. M. Yeiix.n. 



sea water, instead <>i A<|ii;iriuiii tank water, may increase it by as niiu-li 

 as 19'2 per cent.* As ;i rule, however, the effect produced is nut so 

 great as this. 



The developing ova, after impregnation for one hour under normal 

 conditions in ordinary Aquarium tank water, were kept for various 

 periods in diluted sea water or pure sea water, and were then trans- 

 ferred to ordinary tank water again. Once the ova have reached the 

 free-swimming blastula stage, or within about five hours in the middle 

 of the summer, it is practically impossible to separate them from tin- 

 water in which they are swimming. In all the experiments, therefore, 

 one part of the diluted or pure sea water, after vigorous stirring to 

 distribute the embryos evenly through it, was poured into ten parts of 

 the normal water. The subsequent growth of the embryos was there- 

 fore continued in tank water containing an eleventh part of the foreign 

 water, but, as will soon be seen, this could have made very little differ- 

 ence to their size. 



In the first experiment, made in the beginning of April, the develop- 

 ing ova were placed in diluted water made by adding 100 c.c. of fresh 

 water to 1900 c.c. of Aquarium tank water. The specific gravity of 

 this water was found to be 1 '02736 at 15-56' C., whilst that of the 

 unadulterated tank water was 1 '02869. The following were the 

 results obtained : 



Normal larvae (13-8) lOO'OO 



1 6 hours in diluted water ... 95'44 



112 ... 93-55 



125 ... 89-02 



1192 ... 102-08 



Here we see that larvae kept first in diluted water, and then trans- 

 ferred to normal water, are considerably diminished in size, those 

 transferred after twenty-four hours' development being diminished by 

 no less than 1 1 per cent. 



The next experiment was made in July, when the temperature of 

 the water during development was 21-5, or nearly 8 higher than in 

 the April experiment. The following values were obtained : 



Normal larvae (21-5) 100-00 



1 6 hours in diluted water . . . 96'90 



111 ... 96-63 



1-25 ... 103-28 



1144 ... 103-66 



In this case the larvae reached their minimum size after ten hou r s' 

 growth, and then so rapidly increased that fourteen hours later they 

 were 3 per cent, larger than the normal. 



* ' Mittheilungen a. d. Zool. Stat. zu Neapel,' vol. 13, p. 376. 



