Parasitic Crustacea effect their Conservation. 273 
true in this case: either chance presides in this union of the 
-young Crustacean to its mother, or it has nothing to do 
with it. 
On the former hypothesis, as the embryo must be either male 
or female, it is evident ‘that it may sometimes be a male, and 
then matters would go on as above described ; if, on the con- 
trary, it is a female, the conditions of which I have just spoken 
would certainly no longer exist, but this migration would still 
have a very useful purpose, since it would transport from one 
fish to another a young Crustacean, which perhaps might have 
been unable to perform this migration of itself and by its own 
powers, and thus contribute to dissemination, which is one of 
the most essential elements in the conservation of the species ; 
moreover, there is nothing against these females meeting with 
males in their new position. 
The second supposition is the most probable one, in my 
opinion. Indeed, how can we explain the development of so 
extraordinary an apparatus at the anterior part of the frontal 
margin of these young Crustacea without assuming some im- 
portant motive for the production of this modification ? and 
no reason can well possess more importance than the con- 
servation of the species. Moreover it would be very difficult 
for creatures so feeble and so destitute of organs of adhesion to 
maintain their position and resist the action of the waves, which 
is the more powerful in proportion to the rapidity of progression 
of the fish on which they occur. 
However this may be, I leave these facts as ascertained by me 
for the appreciation of those who are willing to seek for their 
solution, which, however, in my opinion, can hardly be other 
than that indicated by me. 
As already stated, the frontal cord is very flexible, especially 
in its middle part; it is hollow, cylindrical, and covered with a 
few hairs, and becomes rigid and brittle near the frontal margin ; 
so that it might be broken before the proper time, if another 
combination had not been made to avoid the possibility of such 
accidents. 
In most of the young Crustacea furnished with this apparatus 
there exists an articulation below the antenne and the eyes, 
which allows this part of the head to bend as if it were borne 
upon a neck; so that by this means sudden and violent shocks 
are avoided, as well as the accidents which might be produced 
by them. A time comes, however, when rupture is neces- 
sary,—namely, when the young Crustacean, becoming able to 
procure its own nourishment, has no longer any need of its 
mother. It then takes place close to the frontal margin, where 
here is a sort of umbilicus, which subsequently diminishes and 
Ann. & Mag. N. Hist. Sev.3. Vol. xiv. 18 
