MOLGULA 237 



fold, the typhlosole, extends throughout the intestine. What 

 is the use of such a fold? 



Reproductive System. — On each side of the body, adherent 

 to the inside of the mantle, is an elongate hermaphrodite 

 gland. Each gland consists of a lighter part, the testis, and 

 a darker part, the ovary. The gonoducts open on the outer 

 wall of the atrial cavity near the base of the atrial siphon. 

 Each consists of two ducts, oviduct and vas deferens. Micro- 

 scopic examination of the oviduct may show the presence of 

 eggs. 



Excretory System. — The renal organ is a conspicuous, 

 elongated sac on the right side. It contains a brownish fluid 

 and usually some solid matter. It does not possess a duct. 



Nervous System. — The cerebral ganglion, which in Mol- 

 gula 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 subneural gland, opens as the dorsal tubercle men- 

 tioned 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 (% 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 cardiovisceral 

 vessel runs to the visceral mass, where it divides into smaller 

 vessels. These, reuniting, form the viscerobranchial 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 



