THE ARTERIES. 167 



3. Olfactory setae. On the ventral surface of each joint of 

 the exopodite of the antennule are two tufts of fine 

 sensory setae. Under a low power of the microscope 

 each is seen to consist of two segments, of which 

 the distal one is much the longer, and is flattened. 

 They are probably olfactory in function. 



III. THE ARTERIES AS SEEN IN AN INJECTED SPECIMEN. 



Bore a small hole in the carapace immediately above the 

 heart : inject with Prussian blue, using a syringe just large 

 enough to fill the hole. Dissect from the left side, removing 

 the left half or more of the carapace, and such parts of the 

 liver, genital gland and duct, and of the side-wall and muscles 

 of the abdomen as may be necessary to expose the following 

 arteries : 



1. The ophthalmic artery is a median artery arising from 



the anterior end of the heart and running forwards 

 over the stomach, then curving downwards to supply 

 the front of the stomach and the oesophagus. 



2. The antennary arteries arise from the anterior end of 



the heart, one on each side of the ophthalmic artery. 

 Each runs forwards, outwards, and downwards over 

 the side of the stomach, to which it sends a gastric 

 artery : and then forwards to the anterior end of 

 the head, supplying the kidney, antenna, antennule, 

 and eye, and sending a branch to the rostrum. On 

 its way it gives off numerous small arteries to the 

 muscles of the regions which it traverses. 



3. The hepatic arteries arise from the ventral surface of 



the heart near its anterior end, and supply the liver, 

 in which they are buried. 



4. The sternal artery is single, and arises from the hinder 



end of the heart, whence it runs directly downwards, 

 passing to the right or left of the intestine, and 

 between the connectives uniting the fourth and fifth 

 ganglion-pairs of the thoracic nerve-chain (p. 163). 



