330 Miller—The Anatomy of the Heart of Cambarus. 
hypodermic syringe, which has been filled with the above solu¬ 
tion, through the muscular wall of the heart into its cavity and 
making steady pressure on the piston. When this method is 
used, the carapace must be removed over the heart and the 
pericardial chamber opened. Successful preparations may be 
made by simply pushing the needle of the hypodermic syringe 
dorsally through the articulation between the cephalo-thorax 
and first abdominal segment, in a forward and downward direc¬ 
tion, until it is within the pericardial chamber, and then press¬ 
ing steadily on the piston. 
The pulsation of the heart may be observed by opening the 
pericardial chamber of a live Crayfish; if this is kept filled with 
normal salt solution, the action of the heart may be watched for 
a considerable period. 
FORM. 
We will first consider the form of the heart as brought out by 
the reconstruction. 
As will be shown later in the paper, the heart from which the 
reconstruction was made was in a contracted condition; this fact 
should be kept in mind while following the accompanying 
description. 
Looking down upon the heart from the dorsal side, its form 
may be described as being saddle-shaped, the most prominent 
feature being the ridge, which runs from the posterior to the 
anterior border, increasing in prominence as it advances, and 
becoming distinctly rounded as it passes between the two dorsal 
openings. (Fig. 1, PI. V.) 
Viewed from the side, two openings into the heart will be 
seen, one placed behind the other. It will also be noticed that 
the dorsal surface of the heart projects some distance beyond the 
ventral, both anteriorly and posteriorly. The sides of the heart, 
are concave dorso-ventrally. (Fig. 2, PI. V.) 
The ventral surface is the shortest; it has no openings into the 
cavity of the heart. It is slightly concave from side to side. 
(Fig. 3, PI. V.) 
In order that the heart may be conveniently studied, especially 
in regard to .its cavity and the relation which it bears to the 
