Parasitic Crustacea effect their Conservation. 275 
the Chondracanthi, on the contrary, are packed together in 
jayers. The eggs never contain more than one vitellus. 
The young Crustacea of these various species do not disperse 
themselves immediately after their escape from the egg; they 
remain for some time fixed upon the oviferous tubes, from which 
they afterwards dart in pursuit of their prey, or establish them- 
selves upon the surface of the fish on which they have been 
hatched. 
They swim rapidly and in gyrations, by means of the six bi- 
ramose feet terminated with long hairs, which they agitate with 
great force. I have remarked that when an opake body is 
‘passed rapidly above the vessels in which they are kept, their 
movements become much more rapid, which leads me to think 
that the shadow resulting from the interposition of this body 
between them and the light produced for them the same effect 
as that of the passage of a fish within their reach, and which 
they endeavoured to seize. 
In the centre of these young embryos we observe the stomach, 
which, not being yet filled with food, appears nevertheless to be 
distended, as if it contained air, and may assist in facilitating 
progression by sustaining them and performing the office of a 
swimming-bladder. 
The young Crustacea, after their escape from the egg, may 
exist without nourishment for from three to fifteen days when 
they are preserved in vessels filled with very pure sea-water and 
kept in a dark and cool place. There are species which live for 
a considerable time; but generally the embryos of the Pandore 
and Chondracanthi die before those of the Trebie and Caligi, 
which, moreover, are more lively in their movements than those 
of the former Crustaceans. I have also ascertained that the life 
of the embryos attached to their mothers by a frontal cord lasted 
much longer than that of those preserved separately in water, 
which they survived for a long time, and even until decomposi- 
tion had set in: this-is a curious fact, which seems to me to be 
evidently in connexion with‘ the prevision which presides over 
the conservation of species. | 
Note.—Since writing this memoir, I found, on the 8th of June 
1863, on the gills of Merluccius vulgaris, a female Chondracan- 
thus, to which two male individuals, arrived at their perfect de- 
velopment, were attached by a frontal appendage. This evidence 
seems to me to convert the hypothesis above proposed by me 
into a certainty, and to confirm my supposition that the males, 
for the purpose of propagation, attach. themselves artificially to 
the females by the singular means which I have described. 
18* 
