184 HUGH WATSON. 



of the intestine. This hepatic ai'tery soon divides into two 

 branches. In A. gibbonsi the anterior branch chiefly 

 supplies the anterior lobe of the right division of the liver^ 

 while the remainder of the right division is supplied by the 

 posterior branch. In A. dimidia the anterior branch 

 supplies the a,nterior division of the liver, while the posterior 

 branch supplies not only the posterior division, but also the 

 hermaphrodite gland which it traverses. In A p e ra b u r n u p i 

 and A. parva the blood-supply of the right division of the 

 liver is similar to that in A. gibbonsi, excepting that 

 the two branches arise separately from the anterior aorta, 

 though very close together. In A. sexangula these arteries 

 also arise separately from the anterior aorta, and their origins 

 are much further apart. 



The anterior aorta passes through the loop formed by the 

 intestine in Apera burnupi, A. sexangula, A. parva, 

 and in A. gibbonsi gracilis and A. g. lupata (PI. IX, 

 figs. 28, 31, and text-fig. 5, d) ; but in A. dimidia, A. pur- 

 celli, A. gibbonsi s. s., and A. g. rubella, the aorta 

 passes straight forward on the right side of the loop (figs. 27, 

 29). It is very remarkable to find this important difference 

 separating forms which seem to be so closely related that I 

 have not ventured to regard them as distinct species. For 

 the difference amounts to this : that in the first group the 

 aorta, on its way from the dorsally situated heart to the 

 ventral ganglia, passes on the left side of the alimentary 

 canal, while in the second group the aorta passes on the right. ^ 



The aorta then runs forward between the digestive and re- 

 productive organs, being often closely applied to the left side 

 of the albumen gland. It gives off to the left three or four 

 ai'teries to the crop and salivary glands, and to the i-ight at least 

 one artery to the albumen gland and another to the common 

 duct, a branch of the latter going forward to the receptaculum 

 seminis. The aorta then becomes more ventrally situated and 



^ A similar variation in the course of the aorta lias been found by 

 Koliler in the ^^enns Siphon aria ('Zool. Jahrb.,' 1893, vol. vii; compare 

 tig. B, p. 27, with figs. A and c, p. 32). 



