264 GILBERT G. BOURNE. 



The Nervous System. 



The nerve-ganglion of Oligofcreina occupies the position 

 typical in Ascidiaus. It was not sufficiently well preserved 

 to admit of thorough histological examination, but there is 

 an external layer of rather large multipolar nerve-ganglion 

 cells surrounding a central plexus of nerve-fibres. Anteriorly 

 three stout nerves are given off from the ganglion, one of 

 which passes straight forward to supply the dorsal part of 

 the sphincter and the dorsal arms. The two other nerves 

 pass right and left of the branchial siphon and supply tlie 

 lateral and ventral parts of the sphincter and the lateral and 

 ventral arms. Posteriorly a single nerve can be traced back- 

 wards for some distance in the mid- ventral line, and smaller 

 branches appear to be distributed to the oesophagus. 



The Subneural Grland and Duct. 



The subneural gland itself was not well preserved. It 

 appears to consist of a few short tubules closely applied to 

 the nerve-ganglion. The interior of the tubules is occupied 

 by numerous small cells with deeply stained nuclei, but the 

 histology of the gland could not be satisfactoril}^ determined. 

 The duct, on the other hand, is large, and the tall, columnar, 

 ciliated cells forming its epithelium were admirably pre- 

 served. The duct is short, and opens by a gaping slit-shaped 

 orifice in the mid-dorsal line of the prebranchial zone. The 

 orifice is situated on a small eminence, the dorsal tubercle, 

 and, as far as could be determined from the sections, it is a 

 simple longitudinal slit ; there is no evidence of the spiral 

 twisting of its lips so commonly found in other Ascidians. 



In conclusion I must call attention to the cavities marked 

 X in figs. 7 and 8. The cavity in fig. 8 is a posterior 

 diverticulum of the larger cavity shown in fig. 7, and this is 

 seen in the latter figure to be continuous with the space 

 formed by contraction of the tissues between the spout-shaped 

 ventral continuation of the branchial siphon and the body- 



