366 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



sumption is strong that their form of eye would be secondary. Emphasis 

 is given to this view by the fact that the same type of eye (horseshoe- 

 shaped) is found in the solitary form of each species, while the chain 

 form of each species has a type of eye peculiar to itself. 



The secondary nature of the " hiigelartig " eye, and of all other sorts 

 found in the chain salpse, and the primitive character of the horseshoe- 

 shaped eye, is conclusively shown by the fact that the eye of the chain 

 individual passes through an ontogenetic stage when in form, though, 

 of course, not in histological character, it closely resembles the horse- 

 shoe-shaped eye of the solitary salpa. 



Professor Butschli's suggestion as to the probable primitive mode of 

 origin of the vertebrate lateral eyes is based upon the secondary nature 

 of the horseshoe-shaped eye and its manner of development from the 

 "hiigelartig" eye. If the latter be overthrown, the former is without 

 foundation. 



The most important point, however, is not that for certain special 

 reasons founded upon the comparative anatomy and ontogeny of the 

 salpa eye, the relations suggested between this eye and the vertebrate 

 lateral eyes, are mistaken. It is fundamentally erroneous to homologize 

 the eye of salpa with the eye of any other chordate. The salpa eye is 

 developed from a highly modified portion of the nervous system, which 

 is not represented in the vertebrate brain. This portion, the ganglion, is 

 derived from the posterior part of the neural canal. The eyes of all 

 other chordates are developed from the walls of the first primary vesicle 

 or its homologue. For further elaboration of this point see page 355 to 

 357 of this paper, and also a brief discussion in my paper, "The eyes 

 and subneural gland of salpa," in the Zoologischer Anzeiger [11 ]. 



