88 BULLETIN OF THE ESSEX INSTITUTE. 



INTRODUCTION. 



The work, the results of which are given in the follow- 

 ing pages, has been carried on in the Biological Laboratory 

 of Tufts College, under the direction of Dr. J. S. Kings- 

 ley, to Avhom the author is deeply indebted, not only for 

 the use of much of the material studied, a considerable 

 part of which was already prepared, but far more for in- 

 valuable aid and encouragement during the preparation of 

 this paper. It is also due to Dr. Kingsley to acknowl- 

 edge the free access to his private library containing a 

 large portion of the literature upon the subject, and to 

 state that the models of the first stage of Amphiuma and 

 the three stages of Necturas were made by him. 



In my account of the development of the chondrocra- 

 nium I have not attempted to treat of the origin of the 

 pro -cartilage cells, but I begin with the first formation of 

 cartilage. These earlier stages have been so ably de- 

 scribed by Miss Piatt ('93, '94) that there seems no ne- 

 cessity to repeat her account, especially as her discoveries 

 in regard to the ectodermal orio;in of the cartilage-form- 

 ing cells were largely made in this laboratory, and have 

 received general support and confirmation in the papers 

 of Kastschenko ('88), Goronowitsch ('92, '93, '93^), 

 Klaatsch ('94, '95) and von Kupffer ('95). 



One object in these investigations was to ascertain to 

 what extent the primary cranial structures throw light 

 upon some problems in the classification of certain Ichthy- 

 opsida. The principal of these problems were these : 



(1) By most students the Caecilians have been recog- 

 nized as a distinct order of Batrachia, but more recently 

 the late Professor Cope in several papers has maintained 

 that these forms were in reality aberrant Urodeles and 



