112 BRITISH TUNICATA. 



is rounded and apparently open in the centre, with a 

 bilobed lid ; but, as this appearance varies in different 

 specimens, it is probably deceptive. 



The alimentary canal (PI. XLII, fig. 2) forms a 

 sigmoidal curve extending- from the bottom of the 

 pallial sac to the base of the excurrent orifice. The 

 oesophagus is well developed and somewhat constricted ; 

 the stomach (PI. XLII, fig. 2) is oval and well defined 

 at both extremities, and the interior is lined with 

 numerous deep, close-set, longitudinal laminae ; the 

 intestine is rather wide and of pretty equal calibre 

 throughout; the anus (fig. 64) is a little contracted 



FIG. 64. FlG - 65. 



d 



FIG. 64. Anal aperture of Styela pomaria. Magnified. FIG. 65. Anal 

 aperture of Styela granulata. Magnified. 



with the rim narrow and broken up into a few obtuse 

 irregular denticulations. 



The reproductive organs (PI. XLII, figs. 2-7) are 

 numerous rounded nodules scattered without much 

 regularity over both lobes of the mantle ; though there 

 is occasionally the appearance of a longitudinal dis- 

 position. This appearance is heightened, if not entirely 

 occasioned, by olDserving these organs through the 

 branchial sac, those underlying the branchial folds 

 being obscured and thus producing the appearance of 

 separation into rows (PL XLII, fig. 1). The male 

 vesicles form a sort of cup around the base of each 

 ovigerous sac (PI. XLII, figs. 3-7), composed of from 

 four to seven segments, each segment being one of the 

 vesicles; from the apices of the vesicles the minute 

 thread-like ducts are seen to pass to the upper surface 

 of the organ and go to unite at the base of a minute, 

 extremely short, nipple -like, orifice, overlying the 



