VAEIATIONS IN THE NUMBER OF VERTEBRA 

 AND OTHER MERISTIC CHARACTERS OF 

 FISHES CORRELATED WITH THE TEMPERA- 

 TURE OF WATER DURINO DEVELOPMENT 



GAEL L. HUBBS 

 Museum of Zoology, University of Michigan 



For several years I have been studying the correla- 

 tions between altered environmental conditions and the 

 number of vertebrae and other segmentally arranged 

 structures in fishes. Johannes Schmidt, of the Carls- 

 berg Laboratory in Copenhagen, has been carrying on a 

 series of intensive investigations (see bibliography) which 

 deal with the same problem, and which are for the greater 

 part rather closely paralleled by my own studies. Both 

 of us have obtained, independently, a rather large volume 

 of experimental and observational evidence indicating 

 that the meristic characters displayed by an individual 

 fish are determined not alone by heredity, but in part also 

 by the environmental conditions, particularly tempera- 

 ture, which prevail during some sensitive developmental 

 period. 



II 



The present study is one of those comprising the series 

 just mentioned. It deals with variations in the number of 

 vertebrae, scale-rows and fin-rays within one year-class 

 and between two successive year-classes of the lake 



shiner," Notropis atherinoides (CjT)rinidaB), and in 

 comparison between the corresponding year-classes of the 

 ''blue-gill" sunfish, Lepomis incisor (Centrarchida3). 

 These variations appear to be correlated with differences 

 in temperature prevailing during the several develop- 

 mental periods involved. 



The material of each species is probably a unit as re- 

 360 



