larvæ, that it may be well to trace, however briefly, what steps have been taken to clear up the matter. Leuckart obtained his negative results by the administration of ripe ova to dogs, rabbits, swine, and mice. The eggs of _Ascaris lumbricoides_ have been kept alive by Dr Davaine for a period of more than five years. I have myself watched the development of their contents in fresh water through all the stages of yolk segmentation up to the stage of an imperfectly-organised, coiled, intra-chorional embryo, and have kept them in the latter condition for a period of three months. According to Davaine (‘Comptes Rendus,’ 1858, p. 1217), the fully-developed embryo is cylindrical, its length being, 1/100th of an inch. The mouth is not furnished with the three characteristic papillæ of the genus, and the tail terminates suddenly in a point. Davaine administered some of his five-year-old embryos to rats, and had the satisfaction of finding a few of these eggs in the rodent’s fæces, with their embryos still living, but striving to emerge. He also gave eggs to a cow, and introduced others into the stomachs of dogs in small linen-covered flasks. As a general result it may be said that the embryos escaped from their shells. Those eggs, however, in which the yolk-segmentation had not arrived at the early embryonal stage remained unaffected. According to Heller, the embryo of _A. lumbricoides_ casts its first skin while still within the egg, and “a subsequent ecdysis probably completes its definitive form” (l. c., s. 615). So far back as 1853 Verloren reared coiled intra-chorional embryos in the eggs of _Ascaris marginata_ within a period of fifteen days in distilled water. I also reared the embryos of this species in fresh water, and kept them alive for a period of nearly a year and a half, at the expiration of which time, and during the warm weather, some few of them succeeded in making their escape. According to Davaine, the eggs of many nematode species will readily retain their vitality though long exposed to dryness, but their yolk-contents will not go on developing during this period of exposure. As regards _A. mystax_, however, Heller remarks that whilst “the eggs have a great power of resisting external influences, their development is not arrested in spirits of wine, chromic acid, or oil of turpentine” (l. c., s. 631). In the case of _Ascaris tetraptera_ of the mouse, embryonic formation goes on in spite of the absence of external moisture. Davaine has noticed the same thing in the oxyurides of rodents. Dryness does not even destroy the eggs of _A. lumbricoides_ and _Trichocephalus dispar_. It would seem, in short, that the eggs of nematodes which normally take up their residence in cats, dogs, and in the carnivora which reside in arid regions, will develop embryos in the egg without external moisture. As before remarked, Davaine thinks it is not necessary that these nematode embryos should pass through