20 ART. 5. N. YATSU I 



about the origin and termination of the nerve fibres among the 

 epithelium. 



From the above description no one would doubt the presence 

 of the otocysts in the adult Lingula, at least in the Japanese 

 form, and my account is confirmatory of Morse's discovery. 



Physiologically the organ just described would probably 

 subserve a static function, as in similar organs found in other 

 animals. The terms " otocyst " "otoliths" are employed here 

 simply in the morphological sense. 



IV. HEART. 



Into the macroscopical feature of the heart I shall not enter, 

 as it has already been fully described by Hancock ('59) and 

 Blochmann ('00). In sagittal sections of the young IAngula 

 (PL IL, Fig. 23, h.) the finer structure of the organ is best seen. 

 In the region which we designate as heart, the blood vessel 

 increases slightly in calibre. The constrictions of the vessel are 

 not constant, varying according to the state of contraction at the 

 time of killing. The vessel is here composed of a tube of 

 columnar or cubical cells and the inner muscular layer. The 

 epithelial cells vary considerably in thickness in different places. 

 As a rule the cell has an enlarged tip, and an attenuated 

 base. The nuclei placed in the middle of the cells are rather 

 compact and stain intensely. Interior to the epithelial layer 

 a thin coating of muscle fibres is found. The fibres do not 

 appear to run longitudinally, but to take a somewhat screw-like 

 course. The movement of the fluid therein contained is due to 

 the contraction of the muscle. At the transverse dorsal ridge of 

 the stomach, upon which the heart is situated, the layer of 



