442 J. GKAHAM KKRH. 



youno- Lepidosiren of the same brood, kept under identical 

 conditions, but killed at 9 p.m., measured from 'OlS mm. to 

 •028 mm. in length, the thickness beino- correspondingly 

 diminished. The difference is seen on comparing fig. 11, M 

 and N. 



The rod rests on the outer end of the visual cell. The 

 inner moiety of the cell is almost completely occupied by the 

 ellipsoidal nucleus. This has a very definite appearance, 

 which marks it oif from the nuclei of the other layers, 

 inasmuch as the chronmtin is collected in large rounded 

 masses, so as to give the nucleus a very coarsely granular 

 appearance. The chromatin network, of which the rounded 

 masses are the greatly thickened nodes, extends equally all 

 through the interior of the nucleus. 



The end of the cell next the rod is occupied by a large 

 spherical vacuole containing a clear fluid. The protoplasm 

 bounding this vacuole is very dense, and stains deeply Avith 

 carmine, forming what looks like a distinct membrane with 

 irregular thickenings. 



As is not very clearly shown by fig. 11, there is associated 

 with the elongation of the rod in darkness a remarkable 

 diminution in the size of the vacuole — a diminution so striking 

 as to suggest the possibility of there being an intimate 

 mechanical connection between the two phenomena, the 

 rod being elongated by the passage into it of fluid from the 

 vacuole. 



Sometimes the wall of the vacuole is in direct contact 

 with the nucleus, at other times the two structures do not 

 touch. 



Between the two is a meniscus-shaped second vacuole, 

 differing from that previously described by its contents not 

 staining black with osmic acid. 



The protoplasm of the cell-l)ody forms ;i thin cylindrical 

 shell round vacuoles and nucleus, while beneath the nucleus 

 it thickens out into a more considerable mass of protoplasm, 

 irregular in shape and giving off prolongations into the outer 

 molecular layer. 



