200 CHORDATA. 



ducts, oviduct and vas deferens. Microscopic examination of 

 the oviduct may show the presence of eggs. 



Excretory System. — The renal organ is a conspicuous, elon- 

 gated sac on the right side. It contains a brownish fluid and 

 usually some soUd matter. It does not possess a duct. 



Nervous System. — The cerebral ganglion, which in Molgula is 

 almost completely surrounded by the subneural gland, lies close 

 to the mantle, between the two siphons, and is thus dorsal to 

 the mouth. Nerves can be seen passing from the ganglion to 

 the two siphons. The hypophysis, a tube leading from the sub- 

 neural gland, opens as the dorsal tubercle mentioned earlier. 



Circulatory System. — 1. The heart, which lies on the right 

 side between the hermaphrodite gland and the renal organ, is 

 inclosed within a pericardium which is a portion of the coelom. 

 It should be studied in a living specimen, with the aid of a hand- 

 lens. 



2. If a very small Molgula (one-eighth of an inch in length) 

 is studied alive in a watch-glass with the microscope, the course 

 of the circulation, and the frequent reversal of its direction, can 

 be observed. 



3. From the dorsal end of the heart a cardio-visceral vessel 

 runs to the visceral mass, where it divides into smaller vessels. 

 These, reuniting, form the viscero-branchial vessel which extends 

 along the dorsal surface of the pharynx above the dorsal lamina. 

 Numerous small branchial vessels in the pharyngeal wall connect 

 this vessel with the branchio-cardiac, which lies ventral to the 

 endostyle and unites with the ventral end of the heart. The 

 frequent reversal of the current can be readily seen both in the 

 heart and in the vessels. 



The relation of the parts will be more clearly understood if 

 a second large specimen is dissected as follows: With scissors 

 cut off the atrial siphon, thus exposing the atrium; then simi- 

 larly remove by a single cut the oral siphon, together with the 

 anterior end of the pharynx (the piece thus cut off should contain 



