332 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



fibers of the optic nerve bind the center of its ventral face to the dorsal 

 part of the ganglion. This primitive condition, which has been retained 

 in Salpa scutigera-confederata, has been altered in Cyclosalpa pinnata, 

 owing to the reversal that takes place during the development of its eye, 

 by which the originally anterior edge of the optic disk becomes posterior 

 and its originally ventral surface dorsal. In this way, in Cyclosalpa 

 pinnata, the optic nerve came to lie on the dorsal face of the posterior 

 part of the adult eye. A comparison of the figures on Plates XLVII 

 and XLVIII will show the manner of this change. A comparison of 

 Figs. 1, Plate LIII; 4, Plate LII; 7, Plate LIII; 1, Plate LIV; 13, Plate 

 LII, and 10, Plate LIV, will show that the manner of innervation of the 

 dorsal eye of the chain Cyclosalpa Chamissonis, Salpa cylindrica, Salpa 

 runcinata-fusiformis, Salpa africana-maxima, Salpa hexagona, and Salpa 

 costata-Tillesii agrees closely with that found in the chain Cyclosalpa 

 pinnata. This can be explained only by the supposition that in all these 

 species there has occurred a shifting during the development of the eye, 

 comparable to that described for Cyclosalpa pinnata. The innervation 

 of the dorsal eye of Salpa scutigera-confederata shows that in this species 

 no such shifting of the eye has occurred. The portion (anterior) marked 

 e' in Fig. 1, Plate LV, is, then, homologous to the portion (posterior) 

 marked e' in Fig. 1, Plate XLIX, and the portions marked e" in the two 

 figures are homologous. The eye of this species is, then, in this regard, 

 more primitive than that of the others. We can say that in respect to 

 position and innervation the dorsal eyes of the chain forms of the other 

 species just mentioned pass through a scutigera-confederata stage. 



SALPA BICAUDATA (?). 



The dorsal eye of the chain Salpa bicaudata (Fig. 1, Plate LVI) is 

 very closely related to that of Salpa scutigera-confederata, chain form. 

 It presents, however, points of difference sufficient to indicate at least 

 a varietal distinction between this and the latter species. The eye is 

 strongly bilobed (Plate LV, Fig. 6) ; the two lobes representing the two 

 regions (anterior and posterior) seen in the dorsal eye of the chain Salpa 

 scutigera-confederata. There is seen the same contrast in the relative 

 position of the pigment layer and the rod cells in the two lobes as in the 

 two regions of the eye of the last species. The two lobes of the eye are 

 not, however, anterior and posterior, as we would expect. A twisting 

 through an arc of forty-five degrees has taken place, by which they are 



