Prof. G. J. Allman on the Anatomy of Actzon. 155 
The general characters upon which the French naturalist main- 
tains the distinctness of his new order of Gasteropods, are the dis- 
appearance in whole or im part of the circulatory system, and the 
transference of the respiratory function from special organs to the 
digestive system or common integument,—peculiarities which he 
asserts draw with them a general degradation of the organism, 
approximating it to the Acalephze, and thus establishing a group 
of animals which depart from the type of their class, and are 
among the Gasteropods what the Entomostraca are among the 
Crustacea. 
The memoirs of M. de Quatrefages are certainly characterized 
by great ingenuity and will well repay perusal. They have how- 
over, I fear, thrown themselves open to justly severe criticism, and 
by advancing statements of great zoological importance upon 
what must be admitted to be imperfect and too manifestly pre- 
judiced observations, would, if not corrected, exercise a most in- 
jurious influence upon a science so strictly inductive as zoology. 
Of the various animals dissected by M. de Quatrefages in the con- 
struction of his Phlebenterate group, Act@on is the only one which 
I have had an opportunity of examining. The result of the ex- 
amination of this one however is so totally at variance with the 
anatomy of the same animal as recorded by the French zoologist, 
that though we can hardly be justified im asserting from this, 
that his observations on the others are equally erroneous, we must 
yet surely hesitate before we adopt conclusions of such great im- 
portance in zoology as those to which M. de Quatrefages has 
arrived. 
On comparing the description and figures of Acteon, as given 
by M. de Quatrefages in the memoir to which allusion has just 
been made, with the structure which my own observation of this 
animal had revealed to me, I was struck with a discrepancy, for 
which I must confess I found it difficult to account by reference 
to any of the ordinary and unavoidable errors to which the obser- 
vation of these minute animals is necessarily liable. 
Among the most important poimts in which the observations 
just recorded differ from those of M. de Quatrefages, may be 
mentioned the detection of a distinct heart and vessels, organs 
whose existence is denied by the French naturalist, and of a /a-— 
teral termination to the intestine, which is described in the fo- 
reign memoir as opening dorsally and medially. The form and 
disposition of the gastric ramifications do not at all correspond 
with M. de Quatrefages’ description; the terminal cu/s-de-sacof this 
system are arranged very differently from the disposition which 
he assigns. to them, and the ramifications of opposite sides do not 
communicate. There is certainly no such organ in the posterior 
