LARVAE OF ARBACIA PUNCTULATA 369 



evident in the stronger solutions. Figure 55 represents a typi- 

 cal individual of the control cultures, and practically all the 

 specimens were in a similar stage of development. The same 

 may be said of solution h (fig. 56). But in solution c, figures 57 

 and 58 represent two of the extreme variants and it may be 

 seen that, although of approximately the same size, both larvae 

 are in a less advanced stage than either of the above. This is 

 true also of those in d (figs. 59 and 60). 



In the stronger solutions, moreover, there enters the element 

 of irregularity of structure, apparent only in the minuter de- 

 tails. In the specimen represented by figure 62 (6, 48 hours), 

 for instance, fusion of the transverse rods would probably not 

 have occurred in the mid-line. In figure 63 (c, 48 hours), one 

 body-rod is longer and heavier than the other, and the indi- 

 vidual elements in the left anal arm are very slightly distorted. 

 In figure 68 (b, 96 hours), the transverse rods are unequally de- 

 veloped and that on the right side seems to have undergone a 

 secondary elongation in order to meet the other. 



This experiment was repeated a number of times and a slight 

 variation was found in the exact time at which the control 

 culture outgrew those in the alkaline solution. In one instance 

 the specimens in solutions b were still of larger size at 48 hours, 

 but by 72 hours, the only apparent difference was the greater 

 degree of symmetry of those of the control. In this set of solu- 

 tions, too, there was less difference in size between the specimens 

 of the control and those of the alkaline solutions at the late 

 stages, — a condition which seemed to prevail in all the experi- 

 ments of the early part of the following year, when the speci- 

 mens in general were more viable, and those in the experimental 

 solutions seemed able to live under more extreme conditions. 

 On the other hand, in experiments when the controls them- 

 selves were less vigorous, the difference in size between them 

 and the specimens in the treated solutions appeared more exag- 

 gerated in later stages, following an earher appearance of the 

 typical irregularities. For instance, figures 71, 72, 73 and 74 

 (Experiment 7) are drawn from the 24 hour stage of specimens 

 from solutions corresponding to a, b, c and d of Experiment 6. 



