150 Miscellaneous. 
No special nerve-fibres could be detected passing to these pig- 
mented grooves. Nerves passing to the eye of Patella were also 
wanting; while, on the other hand, distinct veins were found 
passing to the eye of Haliotis and Fissurella. 
He further stated that this power of distinguishing a shadow 
would be of great use to the animal in the struggle for existence. 
The Solen lies buried perpendicularly in the sand, and allows the 
siphon to project a little above the surface. This projecting part 
would, probably, frequently be bitten off by fishes, were it not for 
the fact that the shadow of the enemy would give warning, so that 
the siphon could be withdrawn in time to save it from destruction. 
—Proc. Acad. Nat. Sci. Philad., Nov. 6, 1883, p. 248. 
On a Nematode Parasitic on the Conmon Onion. 
By M. Joannus Cuatin. 
It is well known that the parasitism of the Nematoda is exerted 
not only at the expense of animals, a certain number of these worms 
attacking various plants, in which they give rise to more or less 
serious alterations. The Anguillula of mildewed wheat has been very 
long known ; an allied species, parasitic on the coffee-tree, has been 
studied by M. C. Jobert ; and other worms belonging to the same 
group are observed in Dipsacez, Mosses, &c., as [ took occasion to 
state in a communication dating some years back. 
The worm which forms the subject of the present note lives as a 
parasite in the common onion (Alliwm Cepa, Linn.), and becomes in 
it the cause of a disease of which I have been able to trace the 
different phases, thanks to the extreme kindness of M. Pasteur, who 
sent me, in May 1881, a portion of a bulb infested by these Nema- 
todes. I have been compelled to defer the publication of the results 
of my researches on account of the time necessary for tracing the 
development and the mode of propagation of the worm, apprecia- 
ting exactly its vital resistance &. Even now I shall confine 
myself to a summary of the principal points of its history ; the ana- 
tomical and embryogenic details &¢. must find a place in a more 
extended work. 
By its general characters and especially the construction of its 
digestive tube, as also by the organization of its reproductive ap- 
paratus, the Anguillula of the onion must be classed in the great 
genus Z'ylenchus, and every thing authorizes our thinking that it 
represents a species distinct from those which have hitherto been 
described. 
It is in the larval state that the worm penetrates into the bulb, 
which it attacks at the level of the “ fundamental axis;” then it 
spreads into the roots and to the base of the flowering stem, gene- 
rally respecting the external tissues, but completely disorganizing 
the central tissue, even getting into the fibro-vascular bundles and 
reducing them to a brownish pultaceous mass, in which nothing but 
a few fragments of spiral vessels is soon to be observed. 
