62 



R. R. HUMPHREY. 



group, as will be seen, are of much smaller average size and do not 

 develop as many lobes as do the animals of the first group. 



The multiple testis being purely the expression of the spermato- 

 genetic wave rate and the time required for lobule regeneration, it 

 follows that conditions modifying these factors will through them 

 modify the form of the testis. Favorable metabolic conditions 

 may increase to some extent the wave rate. The wave will travel 

 farther in a season i.e.., a greater number of lobules of secondary 

 spermatogonia will develop into spermatocytes I. before such de- 

 velopment is checked for the season and a boundary plane estab- 

 lished. As a result the functional lobe will be of greater length 

 than had the wave rate been slower. Lobes of large vigorous 

 males, it is found, tend to be longer than those of smaller speci- 

 mens. Greater lobe length, in turn, acts to reduce the number of 

 lobes that may develop from a germ-cell cord of given length. 

 Increase of the spermatogenetic wave rate beyond a certain limit, 

 clearly, would reduce the number of lobes to one, and a multiple 

 testis would not be developed. 



Unfavorable metabolic conditions, similarly, may still further 

 reduce the normally slow wave rate of Dcsnwgnatlius. This would 



TABLE II. 



LENGTHS OF DESMOGNATHUS MALES OF SMALL DARK TYPE, TAKEN FROM 

 GORGES NEAR ITHACA (Largely from Fall Creek Gorge on Cornell 



University Campus.) 



Arranged in groups on the basis of the type of testis. The type numbers 

 in the first column correspond to the type numbers of the diagrams of chart I. 



