NOTES AND COMMENTS. 165 



Adders and Their Young. 



Readers of Natural Science may remember a note of ours 

 early in the season respecting the alleged habit of young adders, that 

 of taking refuge in the mouth of their mothers. At the time we were, 

 and still are, sceptical as to the habit. But it must be remembered 

 that a large body of tradition and popular belief exists in favour of it, 

 and that more than one naturalist believes in it. There are many 

 districts in Britain where adders are abundant ; for instance, in many 

 parts of the New Forest, in Devon and Cornwall, in Wales, and in 

 the Scotch Highlands. Adders should have their young about them 

 all through August in England, and well on to October in the 

 Highlands. Every naturalist should be on the outlook for them. 

 They are to be found most easily by stealing along hedgerows and 

 ditches in sunny places. Quietness is necessary, as they are easily 

 disturbed and conceal themselves rapidly. The best way to catch 

 them is to pin them between the prongs of a forked stick, and then, 

 with a pair of forceps or small tongs, to place them in a tin case. If 

 it should fall to the lot of a reader to see anything like the supposed 

 habit, he should use every endeavour to secure the specimen. Let it 

 be remembered that it is now too late for verbal testimony — there is 

 enough of that and to spare. The adder must be killed, preserved in 

 spirit, and opened by a skilled naturalist in the presence of witnesses. 

 As we have already said, the Editor of Natural Science will be 

 more than willing to receive any such specimen, and place it in the 

 best hands for examination, giving all due credit to the owner of the 

 specimen. 



Determination of Sex. 



M. de Kerherve has communicated to the Memoives de la Socieic 

 Zoologique (viii., 2) a further account of his studies upon the repro- 

 duction of Entomostraca. He found that with various species of 

 Daphnia kept in captivity, it was easy to provoke the appearance of 

 males among the broods. As long as the conditions of temperature 

 and nutrition were favourable, the daphnids reproduced partheno- 

 genetically and gave rise to females only. The rate of reproduction 

 varied directly with the nutrition. With well-fed daphnids reproduc- 

 tion was so rapid that three or even four generations might be seen 

 lying one within the other, a veritable picture of the old idea of evolu- 

 tion. While the young were yet within the brood-pouch of the mother 

 they had given rise to new generations of young within their own 

 brood-pouches, while in these again the young might be detected. 

 But when the animals were subjected to a lower temperature and to 

 an impoverished food-supply, males were produced in excess of 

 females. 



M. de Kerherve regards these interesting, although not quite 

 novel, results as being quite opposed to Weismann's views. He 



