320 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



that portrayed in Fig. 1), no indication of a division into two limbs is 

 visible. Even in a much later stage (Fig. 6, Plate XL VIII, a vertical 

 cross-section of the eye when it is perpendicular to the brain) no trace 

 of such a division is seen. Later, when the young wheel is formed, but 

 is still attached to the stolon, the division is complete (Plate XLVIII, 

 Fig. 10), though the two limbs of the eye are not separated by so great a 

 space as in the adult. 



While the developing eye is shifting from a perpendicular to a hori- 

 zontal position it remains attached to the ectoderm. The ectoderm is 

 thus folded back upon itself, forming the double fold seen in the adult 

 between the eye and the ganglion. (Compare Plate XLVII, Figs. 5 and 

 7 ; Plate XLVIII, Figs. 1, 5 and 9, and Plate XLIX, Fig. 1.) 



The Small Paired Eyes. 



The two pairs of small eyes are formed at a very late period. No 

 trace of them is found in the chain cyclosalpa still attached to the stolon. 

 Although their development has not been observed, they undoubtedly 

 develop from the small ganglion cells, in the position they occupy when 

 fully formed. Since in them no pigment layer or intermediate layer is 

 distinguishable, the only change in the ganglion cells necessary to pro- 

 duce them would be a modification of certain of these cells into rod cells, 

 after the manner of the development of the rod cells in the large eye of 

 the chain or solitary form. 



THE ANATOMY OF THE EYES IN OTHER SPECIES OF SALPID^E. 



Cyclosalpa Chamissonis. 



The eyes of Cyclosalpa Chamissonis are more closely related to those 

 of Cyclosalpa pinnata than are the eyes of any of the true salpas. In 

 the solitary form the eyes of the two are practically identical. In the 

 chain form the dorsal eye corresponds to the immature dorsal eye of 

 Cyclosalpa pinnata just before the latter is set free from the stolon 

 (Plate LVII, Fig. 8). It has the same position, projecting beyond the 

 anterior face of the ganglion, with only its posterior third lying on the 

 dorsal surface of the ganglion. It is noteworthy that in this species the 

 eye has not bent quite so far forward as in the adult Cyclosalpa pinnata, 

 but is in a position corresponding to that seen in the eye of the imma- 



