PHYLUM CHORDATA 



29 



from this to the extremity of the tail, presenting at intervals slight 

 enlargements from which nerves are given off. An otocyst or 

 statocyst (oto.) is placed in close relation to the cerebral ganglion, 

 and close to it also is a ciliated funnel ; but there is no neural gland 

 opening into the pharynx. In one species of Oikopleura a simple 

 light-perceiving organ, without pigment, is incorporated with the 

 statocyst. In the simple Ascidians, as we have seen, there is a 

 single flattened ganglion, representing the cerebral ganglion of 

 Appendicularia, situated between the oral and atrial apertures ; 

 and the same holds good of the composite forms. Many of the 

 simple Ascidians have pigment-spots, probably of a sensory 

 character, around the oral and atrial apertures. The dorsal tubercle 

 is always present, but varies in shape in accordance with variations 

 in the form of the ciliated funnel, which opens on it usually in 



0.1 / 



FIG. 740. Salpa. Diagrammatic lateral view of the ganglion and neighbouring parts, at. 

 wall of atrial cavity ; br. branchia ; br. ap. aperture of branchia ; c. c. ciliated crests of 

 branchia ; c. /. ciliated funnel ; ejf. eye ; n. gl. gland (paired) that may represent neural 

 gland ; ph. wall of pharynx. (After Delage and He'rouard.) 



conjunction with the duct of the neural gland, of which it forms the 

 terminal part. The opening may be divided into several smaller 

 apertures by fusion of its lips : rarely the duct gives off branches 

 with independent openings. The tubercle with the ciliated funnel 

 is supplied with nerve-fibres from the ganglion, and is probably a 

 sensory organ of some kind. The neural gland is usually below the 

 ganglion, but may be situated above it or on one side. Sometimes 

 it coalesces with it. 



In Salpa and Doliolum there is also a single ganglion (Figs. 

 735, 736, 737, and 740) situated dorsally, giving off nerves to the 

 various parts of the body. Salpa has a single tentacle, the so-called 

 languet (Fig. 737, Ing.), absent in Doliolum. In Salpa there is 

 a median horse-shoe-shaped eye (Figs. 737, 740), and sometimes 

 smaller accessory eyes. In Doliolum an eye is not developed, but 

 there is a pair of otocysts or statocysts. A neural gland and duct 



