THE EARLY DEVELOPMENT OF THE LATERAL 

 LINE SYSTEM OF AMIA CALVA. 1 



CORA J. BECKWITH. 



The earliest stage of the lateral line system of Amia described 

 by Allis ('88) is in an embryo a day after hatching. In this 

 stage the supra-orbital, infra-orbital, opercular-mandibular and the 

 post-auditory lines are well formed but no individual sense organs 

 are differentiated. Wilson ('91) has described for Serranus a com- 

 mon anlage for the lateral line, auditory organ and branchial sense 

 organ. An elongated furrow formed from the inner layer of the 

 ectoderm lies on either side of the neural tube. This furrow 

 becomes divided by transverse constrictions into anterior, middle 

 and posterior parts. The anterior and middle parts are trans- 

 formed into vesicles by the closing together of the lips of the fur- 

 row and become respectively the branchial sense organ and the 

 auditory organ. The posterior part remains as a groove and is 

 converted into the lateral line. 



Wilson and Mattock ('97) describe for the salmon a thicken- 

 ing in the form of a solid cord which behaves exactly as the fur- 

 row in Serranus. It is constricted into three parts, the two an- 

 terior of which form vesicles, while the posterior remains as a 

 cord which is the anlage of the lateral line. Mitrophanow ('93) 

 has described 'a similar condition in selachians. In this case 

 there is a shallow furrow which merges gradually into the sur- 

 rounding tissue, thus giving a less distinctly defined groove than 

 in Serranus. 



The present work was begun with the purpose of tracing the 

 lateral line system in Amia from its first appearance up to the point 

 where Allis took it up (i. e., in embryos a day after hatching). It 

 was thought possible that the anlage was formed and differentiated 

 in Amia as described for teleosts by Wilson and Mitrophanow. 

 The work was done at the Zoological Laboratory of the Univer- 

 sity of Michigan in 1900, under the direction of Professor Jacob 

 Reighard, to whom I wish to express my sincere thanks. 



1 Contributions from the Zoological Laboratory of the University of Michigan, No. 

 114. 



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