SOME EXPERIMENTS ON THE ORDER OF SUC- 

 CESSION OF THE SOMITES IN THE CHICK 



PROFESSOR MARIAN E. HUBBARD 

 Wellesley College 



The experiments described in the present paper were 

 performed at the University of Chicago during the year 

 1903-04, under the direction of Professor F. R. Lillie, 

 to whom thanks are due for much advice and suggestion. 

 In the course of the preparation of the data for publica- 

 tion during the last summer I learned that another in- 

 vestigator, Mr. J. Thos. Patterson ( '07), had hit upon the 

 same problem, and his results appeared before this 

 article could be published. It has been suggested, how- 

 ever, that the work described may be of value in confirm- 

 ing Mr. Patterson's conclusions. 



The problem, suggested by Professor Lillie, was the 

 investigation of the statement, so generally made by 

 embryologists, that, in the chick, somites arise in front 

 of the one which is formed first. An examination of the 

 most important of these statements will make clearer the 

 nature of the problem. The estimates of von Baer ( '28) 

 and His ('68) did not require serious consideration, for 

 they were not based upon a close study of this point. 

 That of Kupffer and Benecke (79), who thought that 

 three or four somites arose in front of the one which first 

 appeared, was founded upon an examination of a rather 

 wide series of embryos, but only in surface view. Miss 

 Piatt's ('89) work rested upon a study of sagittal sec- 

 tions, and as it was altogether a careful examination of 

 the subject, my attention was directed particularly to her 

 conclusions. Briefly, her account of the formation of 

 the somites is as follows: 1 The first cleft divides two 



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