TYPE PROTOCHORDATA. 623 



anus (aw) into the atrial cavity. A thickening occurs along the 

 entire length of the inner surface of the intestinal wall, form- 

 ing the tjphlosole, and a number of branched tubules open- 

 ing into the stomach (s) represent a so-called " liver " or 

 digestive gland. 



The nervous system consists of a single ganglionic mass 

 (ca) lying on the dorsal side of the body near the anterior 

 end and giving off nerves both anteriorly and posteriorly. 

 Immediately below it is a glandular structure, the subneural 

 gland (sn), from which a duct passes forwards to open into 

 the anterior part of the branchial sac, at the base of a well- 

 marked papilla which may possibly be sensory in function. 

 The gland, from its relation to the nervous system and the 

 branchial sac, has been compared to the pituitary body 

 (hypophysis cerebri) of the Vertebrates. 



Sense-organs are but slightly developed, pigment-spots 

 situated in the neighborhood of the branchial and atrial 

 apertures perhaps representing rudimentary eyes, while 

 sensory functions have been attributed to the tentacles, the 

 dorsal lauguets, and the papilla at the opening of the duct of 

 the subneural gland. 



An excretory function has been assigned to the subneural 

 gland, but in addition to this there are found in the visceral 

 mass a number of spherical bodies (ex) without ducts, in 

 whose cells concretions of uric acid are found. These seem 

 to represent excretory organs, the waste material instead, 

 however, of being passed out from the body is stored up in 

 the cells of the organs a condition recalling what is found in 

 some Echiuoderins and, to a certain extent, the arrangement 

 in the Ectoproctous Polyzoa. 



The Tunicates are for the most part hermaphrodites. The 

 ovary is a ramified structure lying in the loop of the intes- 

 tine, and contains a cavity lined with a germinal epithelium. 

 An oviduct is continuous with the ovar}^ and leads toAvards 

 the atrial cavity, opening into it in close proximity to the 

 anus. The testes (Fig. 283, t) are numerous spherical bodies, 

 also situated in the visceral mass, each portion being provided 

 with a duct which joins with others to form the single vas 



