434 
VEllMES. 
pi. 1, both hermaphrodites (the evolution of the male element ordinarily pre- 
cedes that of the female) j the first ordinarily viviparous, the last oviparous. 
Two free-living Nematoids are recorded by Grube as occurring in the 
littoral zone at St. Vaast lallougue. Abh. schles. Ges. 1868-1869, p. 128. 
Gordius rdbustusj Hammond, from Fish Creek, Montana, redescribed. 
Leidy, in Hayden’s Geol. Surv. Montana, p. 382. 
Evolution : biological problems. 
Pairs of Syngamus trachealis in copula infest the trachea of birds, causing 
a peculiar cough, during which slimy masses, containing the eggs, are 
vomited, but often instantly devoured by the bird, in the fieces of which the 
eggs are found in a more or less advanced state of cleavage. In water or 
damp earth these develop into embryos, of which only a small portion escape 
from the shells. Feeding birds with eggs containing live embryos resulted, 
after two or three weeks, in the birds showing evident symptoms of being- 
infested j and on dissection, the Syngamus was found in the trachea. 
Administering to the bird a Syngamus with mature ova did not result in 
infecting it with the parasite ; and the same negative result was obtained 
on feeding it with insects which had been induced to swallow the eggs. 
It is still a matter of doubt whether the Synga^nus is introduced into the 
trachea directly or through the digestive canal. Ehlers (4). 
'Trichosomum. Leuckart’s discovery, that the males (2-6 mm.) of T. eras- 
sicauda migrate into the uterus of the females (17 mm.), and live there 
as parasites, from 2 to 5 in each, is confirmed by Butschli (2). If a 
female contains no males the eggs are not fertilized, but pass through the 
first stage of evolution, and afterwards undergo a fatty degeneration. 
(Organs of copulation are wanting in the female.) 
Leptodera appendimlata lives in Arion ater as larva (mouth and vent 
closed ; tail with two long cuticular bands). If the snail is laid in water or 
stimulated forcibly to muscular contractions, these small nematoids are 
expelled in great numbers, and rapidly develop in the water or any slimy 
substance, the bands are lost, mouth, genital orifice, and vent become 
opened through the casting off of the entire cuticle, generative elements are 
developed, and copulation takes place. The rapidly developing embryos 
do not attain the size of the parasitic generation, want the bands, and are in 
other respects unlike, but adopt the characters of the genus JRhahditis. They 
do not need any change of condition for attaining sexual maturity ; they 
copulate, produce a third generation, &c. In this manner an indefinite 
series of generations may follow, until the nutritive substance is exhausted, 
when encystation takes place. The migration into the snail, and the pre- 
sumed transformation into the Leptodera-iovm of these encysted JRhahditis 
worms, was not observed. Between male and female individuals of the 
Leptodera- and RhabdUis-QQwemiioii no copulation will take place. There 
is some analogy (in spite of the great difference) between this extraordinary 
alternation of generations” and that of Ascaris nigrivenosa. Claus (3). 
Ascaris aistata. The larva in its fii\st stage is provided with a piercing- 
spine ; it afterwards lives without this (but in all other respects agreeing 
with the first stage and with the youngest stages in the pike) encysted on the 
outer surface of the intestine of the bream ; Linstow (7). 
