294 ELEMENTARY BIOLOGY. [CHAP. 



below which it suddenly subdivides into an ante- 

 rior and a posterior branch. 



b. The anterior aorta; a well-defined vessel running 

 parallel with the sacculated portion of the her- 

 maphrodite-duct On entering the body-cavity it 

 passes beneath the first coil of the intestine and 

 the adjacent globular head of the spermatheca 

 (G. § 3 d) ; it then travels to the right side of the 

 body and runs on, beneath the crop, to the anterior 

 extremity. Branches are given off along its course 

 to the genital apparatus, foot, crop, salivary glands 

 and tentacles, with the adjacent integument; it 

 finally perforates the sheath of the nervous system, 

 ending in relation with the floor of the buccal mass. 

 Special branches accompany the rectum and pedal 

 gland. 



c. The posterior aorta; a considerable vessel which ac- 

 companies, at its outset, the first limb of the in- 

 testine. It descends into the visceral sac, and is 

 mainly distributed- to those portions of the ali- 

 mentary canal and its appended glands contained 

 within the same. 



4. The venous system. With the exception of certain 

 well-defined sinuses and vessels detailed below, the 

 venous channels consist mainly of a series of lacunar 

 spaces, in free communication with the"body-cavity." 

 Reference has already been made (Sect. F.) to the 

 lateral pedal sinus, and if, in an uninjured Snail, the 

 point of the injecting apparatus be carefully inserted 

 into this, no difficulty will be found in demonstrating 

 the existence of the vessels here described. 



Having injected the animal, reflect the lung-sac, 



