lUTHOR S ABSTRACT OF THIS PAPER ISSUED 

 iY THE BIBLIOGRAPHIC SERVICE, OCTOBER 13 



CHROMOSOME NUMBER AND PAIRS IN THE 



SOMATIC MITOSES OF AMBYSTOMA^ 



TIGRINUM 



CHARLES L. PARMENTER 



Zoological Laboratory, University of Pennsylvania 



THIRTY-SEVEN FIGURES (nINE PLATEs) 



CONTENTS 



Introduction 169 



Technique 171 



Observations 176 



A. The number of chromosomes 176 



a. Method of determining the number 177 



1. Procedure 177 



2. Clearness and classification of the complexes 178 



h. Possible variation in number in uncounted complexes 181 



c. Abnormal complexes 182 



B. Somatic chromosome pairs 184 



a. Introductory statement 184 



b. Mensuration 185 



1. Types of cells 186 



2. Method. 186 



3. Sources of error 186 



c. Results of measurements 191 



1. Criteria for determining pairs 191 



2. Evidence for the existence of pairs 194 



3. Summary 199 



Discussion 200 



A. Introductory statement 200 



B. Constancy of chromosome number 200 



C. Variations in other Urodeles 206 



D. Variations in other forms 206 



E. Fragmentation 207 



F. Existence of pairs 208 



a. Pairs in the germ cells 208 



b. Pairs in the somatic cells 210 



1. Meves' measurements 211 



2. Delia Valle's measurements 215 



3. Results in Ambystoma tigrinum 216 



c. Constant relative size relations 220 



d. Summary of measurements 220 



Summary of conclusions 221 



lAlso known as Amblystoma. 



169 



