DAPHNIADtE. 
69 
Gruithuisen has published a very interesting memoir 
upon the Baphnia sima of Midler, in vol. xiv of the 
‘Nova acta Physico-Medica Academic Cesarise Naturae 
Curiosorum/ part i, 1828, in which he describes at some 
length the circulation of the blood, as observed by him, in 
this insect. He describes two hearts, arterial and venous, 
and gives a figure, much magnified, of the blood in 
motion.* His figure of the creature itself, however, is not 
very correct, or it is a species different from that of Muller. 
In M, Edwards’s work on the Crustacea, vol. iii, the 
reader will find a description of almost all the species 
known at the time of its publication, and to that we refer 
him, as containing the fullest list of described species 
belonging to this family. 
Anatomy and Physiology, 8fc . — The body is composed 
of two parts, very distinct from each other : the one, much 
smaller and projecting, forms the head ; the other, much 
larger, and consisting of a thorax and abdomen, is con- 
tained entirely within a very slender and delicate shell. 
The valves of this shell are, in most of the species, per- 
fectly smooth round their circumference, but on the 
middle are marked, either with reticulations or deep 
crossed lines, in one or two species, forming a mesh-work, 
or, as Schoeffer says, they are shagreened like the skin of 
a shark. They are open on the anterior margin, and 
united to each other along the posterior edge, as far as 
the extremity, but have no hinge, being as it were 
simply soldered together, to use the expression of Goeze, 
allowing the animal, however, to open and shut them to 
a certain degree at will. In some species these valves 
are prolonged posteriorly to a point, which, at some 
periods of their growth, and in some varieties, is very 
long, in others very short, and in some altogether 
wanting. 
In the head, the covering of which is harder than the 
other portion of the shell, we distinguish the following 
* L. c., t. xxiv, f. 6. 
