NEMATODA 245 



duced 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" (1. 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 f{ 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" (1. 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 Tricocephalus 

 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 nema- 

 tode embryos should pass through any intermediary bearer, and 

 he believes that they are often directly transferred to the 

 stomach of their " hosts " whilst adhering in the form of an 

 impalpable dust to the coats of their bearers, whence they are 

 detached by the animals frequent habit of licking the fur. 

 Davaine' s view has received some support from the observations 

 and experiments of Unterberger with the eggs of Ascaris 

 maculosa. This observer administered eggs of the worm to 

 doves (whose faeces were free of eggs), and seventeen days 

 after found ova in the faeces. 



With the eggs of the Ascaris megalocephala of the horse I 

 performed numerous experiments. I reared the embryos in 



