58 



rectum. In the female the latter also supplies the nidameiital and accessoi'y glands. 

 A pair of vessels (3^) pass to the branchial hearts and their pericardia. An unpaired 

 artery (4^) arises from the left side of the aorta or from the left vessel of the 

 preceding pair to supply the organs of the genital duct, viz. the spermatophoric 

 sac , the vas deferens , the .spermatophoric gland , and the penis in the male , or 

 the oviduct and oviducal gland in the female. After giving off these branches the 

 aorta divides into three terminal arteries , the right , left , and median pallial 

 arteries. The median mantle artery (6^) pa.sses in mesentery-like median fold across 

 the pallial chamber to the lower side of the mantle. It supplies the lower ventral 

 part of the mantle. The lateral pallial artery (5^) passes obliquely across the 

 visceral mass between the peritoneum and the integument to the edge of the 

 pen near the ventral end of the gonad. Here it leaves the visceral mass and , 

 after giving oflf two arteries to the mantle (7^) , expands into a peripheral heart 

 as it enters the mantle. One pallial branch passes forward in the tissues of the 

 mantle ; the other passes backward giving oft' many branches to the mantle and 

 passes through it to the arterial plexus at the dorsal end of the mantle (9^). 

 The trunk (8^) of the artery passes obliquely through the mantle and enters the 

 middle of the base of the fin. As soon as it enters the fin this vessel divides 

 into two branches which pass beside the cartilage to the dorsal and ventral 

 angles of the fin. Some of the dorsal branches anastomose with the vessels of 

 the plexus (U") which covers the anterior dorsal surface of the mantle. This 

 plexus is formed by the anastomosis of these vessels with branches from the 

 lateral mantle arteries (7^) and from the anterior aorta. 



The arteries of all parts of the squid anastomose freely so that an injection 

 from one artery will fill two or three others: for example, an injection from 

 the anterior aorta will fill the median mantle artery and an injection of the 

 right mantle artery will fill the left artery. The walls of the arteries have three 

 coats; an endothelium, a layer of circular muscle fibres, and a sheath of connective 

 tissue. The aortae and their larger bi'anches are peristaltically contractile and their 

 muscular fibres are short, fusiform, and distinctly cross-striated. The muscle fibres 

 of the smaller arteries and arterioles are plain and those of the latter are irregu- 

 larly distributed so that their contraction makes the vessels moniliform. The large 

 veins, readily distinguishable from the arteries because of their thinner walls, 

 are also peristaltically contractile but it has not been determined whether or not 

 the fibres are striated. The arterioles communicate with a complete system of 

 capillaries but there are no blood-spaces or lacunae. The so-called ''peripheral 

 hearts" occur upon all the large arteries that leave the mantle i.e. upon the fin 

 vessels and the terminal branches of the anterior aorta. The peripheral heart is 



