Page:The Zoologist, 4th series, vol 4 (1900).djvu/428

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Various authorities give different figures: thus Dr. Stradling puts the litter at from 15 to 40, M.C. Cooke at 10 to 20. My own experience leads me to doubt very seriously whether Adders ever have forty young at once. I have dissected now a considerable number of full-grown female Adders in young (three this week), one of which I will now describe in detail.

Dissection of Gravid Female.—On Monday, July 23rd, I dissected a large gravid female Adder for the purpose of counting the number of young that had developed. A mesial incision was made from the position of the ovaries to the cloaca, and the skin turned outwards. Both oviducts were full of eggs. The upper and lower ends of the oviducts were tied with string, and the other organs gently separated. Both oviducts were then lifted out of the body cavity. The dissection showed the blood supply very beautifully, and the young were evidently only a day or two from birth. I took a photo of the full oviducts, as one cannot often get an Adder at this stage. The right oviduct contained seven and the left six eggs. (An egg often contains two embryos.) The specimen was such a perfect one that I thought I would preserve it in toto to harden, so as to observe later the precise position of the embryo in the egg. This being so, I could not be quite certain as to their number, but I think it is 19 or 20. The average of this series of dissections works out at thirteen embryos to each female Adder. (The eggs often contain more than one embryo; in this latter case there were thirteen eggs containing the eighteen embryos.) Possibly a larger series of dissections might give slightly different results, but I do not think the difference is likely to be great. To be on the safe side (as far as the question of capacity is concerned), let us consider the average to be fifteen.

This is soon disposed of, as the Adder's gullet is, of course, adapted to its food. There is no difficulty whatever for a Mouse, a young Water Vole, or a Blindworm to pass into the gullet, and it is quite easy to press them out again if they are contained therein. (A short time ago I killed an Adder which appeared