68 ART. 4. — N. YATSU : 



conclude that they cannot be nephridia, since they do not possess 

 the most essential features of an excretory organ, such as 1) the 

 duct, 2) an opening (nephrostome), and 3) excretory cells. 



The otocyst, it should be noted, persists as such throughout 

 life, showing no sign of degeneration. As to the otocysts in 

 the adult I shall fully describe them in another paper (See Art. 

 5, this volume). 



/.'. Ganglia. 



My results on the nervous system of the larvae of Lingula 

 differ very much from those of Brooks, the chief point being 

 that I have failed to discover the presence of a complete nerve- 

 ring around the oesophagus, containing the ventral and lateral 

 ganglia, as has been maintained by Brooks. 



At the 5-6 p. c. stage the epidermis of the anterior and 

 well rounded-out body- wall, ventral to the neck, becomes marked 

 out into a definite area, and here arise three eminences, one 

 central and two lateral. The central eminence becomes the ventral 

 ganglion (Infra-œsophageal ganglion) (PL VI., Fig. 82, vt. gn.) 

 while the two other smaller eminences, which are situated more 

 dorsally, one on either side of the ventral ganglion, become the 

 lateral ganglia {It. gn.). The relative position of the lateral and 

 ventral ganglia will be best understood by comparing two sections, 

 one transverse (PI. VIL, Fig. 113) and the other longitudinal 

 (PI. VIL, Fig. 94). As the lateral ganglia are formed in direct 

 continuity with the ventral ganglion, they cannot, as Brooks 

 believed, be connected by means of nerve fibres. 



At the 7-9 p. c. stage the ventral ganglion becomes more pro- 

 minent (PI. VI., Fig. 85 ; PI. VIL, Figs. 93, 105). It is best 



