148 Prof. G. J. Allman on the Anatomy of Acteon. 
but whether this is destined to receive from the cesophagus a por- 
tion of the alimentary matter, thus performing the office of a crop, 
or whether its function is that of simply discharging into the ali- 
mentary tract some peculiar product of secretion, I have been 
unable to determine. 
But perhaps the most remarkable of all the organs accessory 
to digestion is the singular ramified system which constitutes so 
large a portion of the viscera of Act@on, and which M. de Quatre- 
fages, conceiving it to be of high importance, has assumed, along 
with certain other peculiarities of structwre which he supposes 
invariably to accompany it, as entitling him to unite into a new 
order a certain number of Gasteropodous Mollusca, distinguishing 
them under the name of Phlebenterata. 
The system under consideration consists in our mollusk of two 
tubes which open, close to one another, into the stomach, at its 
cardiac extremity. Near to its termination in the stomach each 
tube divides into two branches, one, Pl. VI.’ k, passing forwards 
towards the head, the other, //, running backwards into the late- 
ral expansions. Hach of these branches then undergoes minute 
subdivision, the ramifications extending forwards nearly to the 
anterior margin of the head, and backwards to the posterior ex- 
tremity of the lateral expansions. The ultimate ramuli termimate 
each ina cul-de-sac, mmm, and PI. VII. fig. 4, filled with a green 
or brownish substance, in which the microscope enables us to 
detect oleaginous globules floating through a fluid of aqueous 
consistence. 
It is to this curious system, visible through the semitransparent 
integuments, that the prevailing colour of the species must be 
attributed ; its nature and function, and its claim to constitute a 
character of ordinal importance, will be presently considered. 
Vascular and Respiratory systems.—The best way of detecting 
the vascular system of Actgon is to view the mollusk as an opake 
object by means of a single lens and without compression, when 
a delicate ramification of vessels will be seen creeping over the 
upper surface of the foliaceous expansions, Pl. V. fig.4. Those 
vessels which spread themselves over the posterior part of the ex- 
pansions terminate in two trunks, a a, one for each lateral half, 
which running nearly parallel to the mesial line and at a short 
distance from it, at either side appear to end in a circular canal, 3, 
into which the vessels from the anterior part of the expansions 
also open. This circular vessel cannot be satisfactorily seen with- 
out actual dissection ; it is placed immediately beneath the inte- 
guments of the back and over the posterior part of the body, and 
embraces an organ, c, of an irregularly semicircular figure, into 
whose structure strong fibres may be seen to enter with a reticu- 
lated arrangement. Beyond this point my researches have failed 
