SPERM ER UE ETIN A E CV RENT 
ON THE ANGUILLULIDA. riri 
of the genital organs from that above mentioned; those of his second, including Filaria, 
Spiroptera, &e., are distinguished “par la présence de deux organes copulatoires, ou 
pénis, imégaux,” whilst of his third section, containing the genera Strongylus, Leptodera, 
Dicelis, &c., the members of which do possess two equal spicules, with or without acces- 
sory pieces, the genus Leptodera is the only one affording also the character of a uterus 
divided into two equal and opposite branches, with the vulva occupying a median position. 
This genus contains one species‘, the 2. flexilis, found in the vas deferens of Timax 
cinereus. In his fourth section, comprising the Ascarides, the members of the second 
subgenus, Ascaridia, including several species found in the intestines of birds, comply 
with the requirements so far as the male intromittent organs and double uterus are con- 
cerned, but differ by the presence of the three prominent cephalic lobes and the filiform 
ovaries characteristic of the genus Ascaris. In his fifth group, Dujardin places these 
free Nematodes together with certain other genera. The sixth section, containing Sele- 
rostoma, Syngamus, &c., contains only one genus, Angiostomum, having the before- 
mentioned arrangement of the male and female sexual organs; but the figures given 
by Dujardin of the only two species of this genus—one found in the lungs of Anguis 
fragilis?, and the other in the intestine of a pulmonate Gasteropod—seem to indicate a 
totally different formation of the ovarian tubes. The individuals of the seventh and last 
section, including the genera Dacnitis, Ophiostoma, &c., are out of the question, from 
their not. possessing a terminal mouth; and those of the appendix do not comply with 
other conditions ?. 
This evidence seems a sufficient warrant for the belief in the non-parasitie nature of 
the animals in question, since it could scarcely happen, if these forms were ever para- 
sitie, that they should not some of them—or, at all events, species of the same genera 
—have been met with in this condition, so as to enable us to include in the same genus 
parasitic and non-parasitic types. To me, indeed, it seems clear that these free Nema- 
toids themselves, which can be detected in all stages of growth in external media, are 
not likely, as a rule, to be capable of existing also as parasites. 'Then comes the question, 
are they as a group distinguished by any particular characters from the parasitie forms ? 
To which I think we are fairly entitled to return an answer in the affirmative, after the 
statements that have just been made, and from a consideration of other facts to be 
presently mentioned‘. So far, too, this is in accordance with the views held by the 
* Another and much larger species has since been found by Dr. Baird in the abdominal cavity of Siredon mezicanus 
nn Zool. Soc. 1858, p. 225, ( Annulosa) pl. 52. f. 6, 7. 
This species, Angiostomum entomelas, I have lately discovered, and have satisfied myself, not only that it does 
eu to any of the genera of free Nematodes at present known, but that it is distinguished from the members 
h ne generally by the form of its ovaries and the extreme thinness of its integument. 
“Ae genus Odontobius being the only one concerning which there is any doubt, the nature of which will be 
PINE in the systematic portion of this memoir. | à e 
la = u that a few of ae free Nematodes have been found see the intestines of ag animals a = : 
np e cases related by him, their presence within the intestinal canal "ay be — ar as ind 2 cone 
re they having been swallowed, as he suggests, by these animals either = or as fo iei a e ori = 
intestine of en by him in the intestine of the Carp. - has mn deli A x didi ok dik egi 
level fishes ana ; 3 and of the common Frog (which, in its turn, swallows the stug), D ipi 
> e general cavity of the body of the Earth-worm. Tt would be desirable to 
