EvcleshvmeR'Davis, Mpiphvsis and Paraphyiis in Amia, 6$ 



reference to the accessory evagination, the paraphysis of 

 Selenka. the anterior epiphysis of Eycleshymer, the ependyma 

 of Hoffmann, all are in front of the epiphysis proper, while in 

 Squalus, according to Locy, it is the pair of eye cups behind 

 the ones that develop into the epiphysis that is wholly lost by 

 degeneration. Of course it does not necessarily follow that be- 

 cause the first pair behind the lateral eyes becomes the epiphy- 

 sis in Selacheans the same would be true in Teleosts, where 

 we know (Hill, '91) that an anterior secondary evagination forms 

 and has a transient existence ; nor in Amphibians where the 

 same thing takes places (Eycleshymer, '92). 



In Lacertilia the difficulty is made still greater by the fact 

 that the secondary evaginations are not only in front of the 

 epiphysis but also that in some species (Leydig '91) there is 

 more than one." From the evidence thus far adduced it would 

 seem appropriate to conclude in the words of Ritter : "Our 

 knowledge of the whole subject is so fragmentary that general- 

 izations based upon it and made in the light of Locy's interest- 

 ing observation, must be very unsatisfactory. One of this au- 

 thor's conclusions is that the epiphysis is homologous with the 

 lateral eyes. But in connection with this conclusion he remarks 

 parenthetically that its "differences in structure need to be ex- 

 plained." This remark is timely and may well be extended to 

 numerous other difficulties involved in the subject." 



Before we can explain the condition observed in certain 

 Reptilia (Leydig) we must either find several pairs of "acces- 

 sory optic vesicles " lying in front of Locy's first pair, or ex- 

 plain how several pairs of those lying behind have come to lie 

 in front. This done the next thing will be the explanation of 

 how the anterior pair of the entire series came to give rise to a 

 pair of widely separated lateral eyes ; one or more succeeding 

 pairs became rudimentary ; how the next in order coalesced to 

 form a median eye ; and the remainder degenerated. 



Concerning the early development of the epiphysial struc- 

 tures in Teleosts we knew practically nothing until the publica- 

 tion of Hill's observations on certain Teleosts and Amia. Hill 



