146 LILIAN SHELDON. 



close to the wall of the cavity, but does not appear to open into 

 it. It is possible that when the spermatozoa become ripe they 

 pass down the duct into the cavity by an opening, which is 

 temporarily established into it, the communication being closed 

 at other times. 



The ovary (fig. 14, 0) lies on the opposite side of the cavity. 

 It has no limiting membrane, the ova lying freely in the 

 pseudoccele. There is no oviduct, but the ova, when ripe, 

 probably break through the wall into the cavity, which thus 

 serves as the common generative duct, conveying both male 

 and female products into the atrial cavity. 



Each ovum is surrounded by a single layer of cells, which 

 either are follicle cells or give rise to the test. 



The Nervous System. 



The nervous system has the form generally found in adult 

 Ascidians. It consists of a large ganglion lying between the 

 mouth and atrial pore, and is composed of fibres, which are sur- 

 rounded by a peripheral layer of ganglion cells. Anteriorly it 

 sends off two nerve-trunks, which pass, one on each side of the 

 mouth ; posteriorly it also sends off two trunks, which very 

 soon divide again into several small branches, whose course I 

 could not follow for any distance. 



The Hypophysial Gland. 



The hypophysial gland is a compact mass of tissue, lying 

 immediately ventral to the ganglion. It consists of a great 

 number of fine glandular tubes, which towards the dorsal side 

 of the gland unite, forming larger ducts, which open into the 

 canal of the ciliated pit. 



