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Pi 
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| #899 900.] Report of the Microscopical Section. 127 
walls of the heart are pierced by six small holes, of which 
two are on the tergal aspect, two on the ventral, and one on 
| _ to the tube of the artery. 
_ The principal arteries which radiate from the heart are the 
following: the superior abdominal artery, arising from the 
in testine, giving off many branches; the ophthalmic artery, 
arising from the anterior end of the heart and passing for- 
_ward above the stomach, giving off branches to the eyestalks 
| and adjacent parts; the sternal artery, arising in the junction 
_ of the superior abdominal artery and the heart and passing 
directly downwards to the nervous system, where it sub- 
divides into an antero-ventral, which passes forward, giving 
off branches to the various appendages surrounding the mouth; - 
and a postero-ventral, which passes backward to the telson, 
giving off branches to the intermediate parts; the antennary 
artery, arising at the junction of the ophthalmic artery and 
the heart and passing downwards and forwards to the antenne. 
The cavity of the heart, and the space between the heart 
and the walls of the pericardial sinus, are filled with blood. 
surrounding blood in the pericardial sinus flows in through the 
small apertures in the walls of the heart to refill the cavity, 
and it is prevented from returning by the valves on these 
apertures. Thus by the expansion and contraction of the 
heart a constant flow of blood is maintained from the peri- 
cardial sinus to the cavity of the heart, and from the cavity of 
the heart to the arteries. 
_ The blood thus forced into the arteries finds it way by their 
 yarious ramifications into sinuses or channels, by which it is 
conducted to the gills. These blood sinuses may be considered 
as analogous to the veins in the higher animals. The blood in 
