No. 3-] THE VERTEBRATE HEAD. 547 



sensillae in about the same condition. In no other species 

 hitherto described do we find the sensillae passing by such 

 gradations into the principal eyes. The serial homology of 

 these organs with the eyes is, then, a fact demonstrated not only 

 by the embryological development, but also by the structural gra- 

 dations exhibited in the adult animaV (pp. 391, 392). 



The existence of a series of rudimentary sense-organs in 

 Vertebrates was brought to light in 1885 by Froriep and Beard. 

 While it is by no means clear that they are the homologues of 

 the sensory papillae of annelids, it is nevertheless probable. 

 It is now generally admitted that they constitute the basis 

 from which the higher sense-organs of Vertebrates are derived. 

 These organs are arranged in longitudinal series. The series 

 has become rudimentary or lost in the adult forms of higher 

 existing Vertebrates, but they are present in the embryos. 

 Kupffer and others have shown that there are at least two 

 series of these organs, the upper one corresponding to the 

 lateral line of comparative anatomy, and the lower one embrac- 

 ing the so-called branchial sense-organs of Beard. From the 

 upper series the ears and nose are probably derived, and possi- 

 bly the eyes. 



Allis ('88), in his well-known memoir on the lateral line of 

 Amia, gives figures that show a connection between the epi- 

 thelium of the nasal pit and that of the lateral line. His Fig. i, 

 PL XXX, representing a larval form one day old, shows the 

 nasal epithelium forming part of the lateral line. In subse- 

 quent growth it follows the same course that the surface organs 

 of the lateral system do when they become canal organs. Allis 

 says, p. 537: "The nasal pits are inclosed in the same way 

 that the lateral canals are, and the short canal so formed is at 

 first continuous with the canal inclosing organ 5 infra-orbital." 



There is now general agreement that the ears belong to the 

 lateral line series, but there has been much dissent on the part 

 of some morphologists to admitting the eyes to the same cate- 

 gory; but the grounds for the opposition seem to me to be 

 largely removed. It must be said, moreover, that the organs 

 of taste and touch have not as yet been shown to have any 

 genetic relation to the ganglionic sense-organs. 



