History of the Nematode Worms. 449 
less doubtful about this, because in S. hypostomum of the sheep*, 
the eggs of which pass out in a state of segmentation, I observed 
Rhabditis-like young in the course of a few days, and these dif- 
fered from the embryos of Dochmius trigonocephalus only by a 
somewhat larger size (0°46 millim.) and an extraordinarily long, 
subulate caudal extremity (of fully 0°15 millim.). The animals 
lived in mud for-several weeks, but only increased a little in size 
(to 0°53 millim.), and then, towards the end of the third week, 
underwent a change of skin, in which the tail was lost. As the 
dental apparatus of the posterior pharyngeal bulb had previously 
disappeared, and the two dilatations were not very prominent, 
the embryo at this period of development (length =0°46 millim., 
of which only 0:04 was due to the abbreviated tail) had a great 
resemblance to the embryos of Strongylus filaria. Unfortunately 
I did not succeed in observing the further metamorphoses. The 
worms remained unaltered in water, and gradually began to die 
off; so that I was induced to administer the remainder of them 
at two different times (on the 20th and 27th of February) to a 
young sheep; but on dissection (on the 6th of March), I could 
not find any trace of them. It is therefore possible that the 
life-history of our Sclerostomum is more complicated than that 
of Dochmius, and that its free existence is not followed imme- 
diately by parasitism in its definitive host. 
The Strongylide with a buccal armature are not, however, the 
only Nematoda with Rhabditiform embryos. ‘The same young 
forms recur in other species, even systematically distant—for 
example, in Ascaris acuminata of the frog, the embryos of which, 
as is well known, are developed in the body of their mother, and 
have been kept alive for a long time in water by Goéze and Du- 
jardint. On close examination, we recognize in these embryos 
the Rhabditis-form above described, with teeth in the posterior 
pharyngeal dilatation, and a pointed but short tail. The length 
of the little worm is 0°6 millim., and its thickness 0:035 millim.; 
the embryo has consequently a tolerably thick form. But this 
appearance is altered in the course of a few days. The embryo 
grows, and, indeed, so rapidly that in a week the length of its 
body has increased almost threefold (nearly 15 millim.). But 
* Tt may be mentioned, in passing, that this Sclerostomum, which in- 
habits the colon, belongs, like Oryuris curvula, to the dung-feeding Nema- 
toda. In the buccal cup and intestine we constantly find numerous vege- 
table particles derived from the vicinity; these form black excrements, 
which accumulate at the anal orifice, and in the females form an incrusta- 
tion surrounding the whole abdominal extremity like a hood. 
+ The same is stated by Spencer Cobbold of Ascaris osculata and A 
megalocephala, but probably, as regards the latter, incorrectly ; for I have 
preserved its eggs, with the embryos contained in their interior, unchanged 
in water for two years. 
Ann. & Mag. N. Hist. Sev.3. Vol. xvii. 29 
