104 ESSENTIALS OF ZOOLOGY 



property, when the circulation stops, or when the blood 

 escapes, of becoming round and viscous peripherally, increasing 

 in size at the same time, and throwing out long filamentous 

 pseudopodia, in which an active circulation of granules may 

 be witnessed. The pseudopodia fuse with one another and 

 entangle neighbouring cells, thus forming a plasmodial clot. 



The blood flows in the spaces around the tissues and 

 organs ; these sinuses or lacunae culminate in the large ventral 

 or sternal sinus in the ventral part of the thorax ; from the 

 ventral sinus the blood is sent to the gills, and from the gills 

 to the pericardial sinus in the upper region of the thorax ; 

 the heart is moored in the middle of the pericardial sinus, 

 from which it receives the blood through the ostia and trans- 

 mits it once more to the body. The heart is attached to the 

 carapace by fine muscular threads on each side, and lies other- 

 wise freely in the pericardial sinus. It is sub-hexagonal in 

 shape, and its muscular wall is perforated by six apertures 

 the ostia two dorsal, two lateral, and two ventral (fig. 49, B). 

 These admit the blood from the pericardial sinus, and the thin 

 lip-like pair of valves with which each is provided prevents the 

 blood from passing outwards during contraction. The heart 

 beats twenty to thirty times a minute, and propels the blood 

 into the arteries. Anteriorly three vessels leave the heart close 

 together, a median one, the ophthalmic, and the paired antennary 

 arteries. The former passes forward over the stomach and bifur- 

 cates to supply the eyes and the front of the stomach. Each of 

 the antennary arteries runs along the side of the stomach, giving 

 off gastric branches, and, reaching the front of the stomach, 

 it supplies the antennae, the antennules, the rostrum, and the 

 green gland. The heart also yields anteriorly from its ventral 

 surface the paired hepatic arteries to the digestive gland. At 

 the posterior end of the heart a vessel arises and immediately 

 divides into (1) the median, dorsal abdominal, which runs 

 backwards along the dorsal side of the intestine, giving off 

 branches in each segment to supply the muscles, intestine, 

 etc. ; and (2) a sternal artery, which passes directly downwards 

 and, passing between the commissures which unite the third 

 and fourth pereiopod ganglia, divides into the anterior and 

 posterior sub-neural arteries, which yield paired branches to 



