M. Coste on Fresh-water Polypi. 71 
covery to the shores of Italy, for the purpose of collecting mate- 
rials for the completion of my treatise on Comparative Embryo- 
geny, I take leave to present to the Academy some results of 
a general work upon the Organization and Natural History of 
the Lower Animals,—a publication which I shall have the 
honour to submit in its complete form when all the plates are 
finished. In the mean time, I shall dwell only on the Fresh- 
water Polypi; and hence this communication is to be consi- 
dered merely as a minute fragment of more extended researches. 
The points upon which I wish at present to fix attention are 
the following : The muscular apparatus is composed, 1st, Of 
the motor tubercular muscles, which are of two sorts,—the one 
flexors within the parts, the other flexors without: they exist 
throughout the whole extent of the tentacula, and present, in 
the course of their progress, a certain number of nodosities or 
knots. 2d, Of the motor muscles of the tongue, which are 
disposed in two parallel series before and behind, and are used 
in raising the organ. 3d, Of the retractors of the animal, 
forming two large muscles, which, from the bottom of the cell 
into which they are inserted, somewhat in advance of the point 
of attachment of the ovary, mount up on each side of the in- 
testine, to which they send fibres of insertion in passing, and 
which, on reaching the middle of the cesophagus, divide into two 
unequal bundles; the larger attaches itself tothe sides of the buc- 
cal aperture at the base of the arms, and the other at the pos- 
terior of the base of these arms. In the Paludicella, the two 
fasciculi are not divided, the fibres being distributed and in- 
serted round nearly the whole circumference of the mouth. 
4th, Of the proper retractors of the intestine, two in number, 
fixed, on the one hand, behind the point of insertion of the 
ovary, and, on the other, at the posterior part of the stomach, 
where they appear to terminate, after bifurcating. 57h, Of 
the dilating muscles of the sheath. These are cutaneous, ar- 
ranged more or less transversely, and very numerous, in a 
certain extent of the length of the circumference of the free 
extremity of the cell. They are inserted, in one part, at the 
internal surface of the skin which covers the extremity of the 
cell, so, of course, favouring the exit of the animal by over- 
