2 METCALF. [VOL. I. 



gland, which I have called the rapheal duct. In different spe- 

 cies the rapheal nerve may arise from the cellular cortex of the 

 brain, from the neural gland, or from a mass of cells formed by 

 the fusion of the brain and the gland. The five accompanying 

 diagrams show some of the conditions found. 



In Cynthia papillosa, Fig. i, the rapheal nerve arises from the 

 cellular cortex of the brain. Alongside it in the raphe is found 

 the unusually large rapheal duct, which has extended down from 

 near the posterior end of the epineural gland. The rapheal 

 duct and rapheal nerve are wholly distinct. 



In Distaplia magnilarva, Fig. 2, there is no rapheal duct. 

 The brain and neural gland are united posteriorly. The rapheal 

 nerve arises from the cortex of the brain, a little behind the 

 point of fusion of the brain with the gland. 



In Amaroecium constellatum, Fig. 3, we find a rudimentary 

 rapheal duct starting back from the gland, but it looses its lumen 

 before going far, and then its cells become united with the 

 cells of the brain to form a common mass of cells whose origin, 

 whether from the brain or the gland, we are unable to determine. 

 From this common mass of cells \.\\Q ganglion cells of the rapheal 

 nerve are derived, its fibers coming from the right posterior 

 siphonal nerve. 



In Ascidia atm, Fig. 4, we have a similar origin for the fibers 

 of the rapheal nerve, but find an interesting difference in the 

 derivation of its ganglion cells. A cord of cells pushes out from 

 the dorsal surface of the brain, near its posterior end, and, after 

 running back a short distance, unites with a backward prolonga- 

 tion of the gland, which runs up to meet it. The prolongation 

 of the gland is evidently the rapheal duct. The two cords fuse 

 immediately, the duct loosing its lumen. The single cord of 

 cells thus formed runs back some distance and then bends 

 down to accompany the fibers of the rapheal nerve. Its cells 

 soon become loosely arranged among these nerve fibers and 

 are clearly the ganglion cells of the rapheal nerve. 



In Pkallnsia mammillata, Fig. 5, these organs are exactly 

 similar, except that the prolongation from the dorsal surface of 

 the ganglion does not unite with the rapheal duct, but bends for- 

 ward, soon ending blindly. In this species, then, the ganglion 



