178 



SCIENCE. 



[N. S. Vol. XI. No. 266. 



spines vary eonsiderablj' io number on in- 

 dividual specimens, but tlie average number 

 on specimens from salt water from diiferent 

 localities is quite constant, being about 

 thirteen. When this shrimp is found in 

 brackish water, however, the averages from 

 different localities vary considerably, and 

 are always less than the salt water average. 

 In water which was nearly fresh, we have 

 found the average to be as low as 9.61. 

 Moreover, the decrease in the average seems 

 to be in proportion to the decrease in den- 

 sity. This seems to show that such a 

 character as rostral spinosity may be so 

 correlated with the economy of the animal, 

 that such a factor as salinity may deter- 

 mine it. The experiment of putting the 

 animals from salt water directly into fresh 

 water failed to show that those whose 

 average number of spines was the least, had 

 the greatest resistance capacity. Hence it 

 is suspected that the direct action of envi- 

 ronment, and not natural selection, is the 

 method by which the evolution to the 

 brackish-water form is accomplished. This 

 question can be settled only by rearing the 

 salt-water form in fresh or brackish water. 

 The decrease in spinosity of the brackish- 

 water form makes it seem probable that our 

 fresh water species, P. exilipes, has been 

 derived from P. vulgaris. The two species 

 are very similar and, at least in respect to 

 rostral- spinosity, intergrade perfectly ; for 

 the averages in exilipes are found to vary 

 from 8.53 to 10.11, while P. vulgaris, as 

 shown above, may have as low an average 

 as 9.61. Experimentation may also throw 

 light on the question as to whether P. exi- 

 lipes has arisen as a variety in one place, 

 and later spread, or has originated in differ- 

 ent places under a common factor of en- 

 vironment — lessened density. In one case 

 where the two forms were found inhabiting 

 the same river (The St. Johns, Fla.), they 

 were separated by a distance of only thirty 

 miles, at most. 



Variations and regeneration and Synapta 



Inhaereus. 



The characters of this holothurian as 

 described in systematic works, were sub- 

 jected to quantitative analysis. The stan- 

 dard deviation, mean, mode and coefBcient 

 of variability were determined for 850 vari- 

 ates of the anchor and anchor-plates, 13 

 variations from the typical anchor and 20 

 variations from the typical anchor- plate 

 were described. The typical anchor pre- 

 vailed in 96.6% of the variates and the 

 plate in 61.5%. 



The specimens examined from Beaufort 

 and Naples showed only one type, that of 

 the described anchor and three types of 

 plate with an adherence of 95f % to the 

 typical form. The specimens from south- 

 ern waters are therefore least variable 

 while the striking divergence is shown in 

 the northern collections from Long Island, 

 and Woods HoU with 18 types of plates, with 

 8 types of anchors showing spurs of various 

 kinds, there is shown a tendency toward a 

 place-mode at Lloyds Harbor, Long Island. 



In one specimen from Centre Island, 

 Cold Spring Harbor, Long Island, 61 3-7% 

 of the variates belong to another than the 

 type-pattern. Similar variations in the 

 number of tentacles with their relation to 

 the normal symmetry were noted. The 

 mode of distribution of digits is three on 

 the dorsal and ventral sides, respectively. 



Nine out of 17 experiments on regener- 

 ation of the body and tentacles were suc- 

 cessful. 



The effect of strychnine on the unfertilized eggs 

 of the sea-urchin : T. H. Morgan. 

 When the unfertilized eggs of Arbacia are 

 placed in sea water containing strychnine 

 they will begin to segment in the course of 

 three or four hours. Strychnine, either as 

 an alkoid or as a sulphate, produces the 

 same effect ; the solubility of the latter be- 

 ing nearly a hundred times greater than 



