262 Variation in the Mealworm, Tenebrio molitor 



A general survey of the principal results obtained with these in- 

 vestigations, leads to the following : 



Summary. 

 I. The Larva. 



1. In nearly every population of larvae of Tenebrio molitor bought 

 in the trade, two colour varieties are found, viz. the CB larva (chestnut 

 brown) and the OR larva (orange red). 



2. As a rare exception a third type may be met with, viz. the BA 

 larva (black abdomen), which is distinguished from the two above- 

 mentioned ones, in that its colour is still darker than the GB larva. 



. 3. The most conspicuous larval anomalies exhibit themselves : 



as a development of the rudimentary wings ; 

 as a partial fusion of the segments ; 



as a variation in the number and position of the spines occurring 

 on the last segment, 



4. The variations mentioned in 1 and 2 are hereditary, those in 3 

 are not. 



5. The duration of the larval stage, under otherwise favourable 

 nutrition-conditions, is in a high degree dependent on temperature. 

 By raising or lowering the temperature the duration can be considerably 

 shortened or lengthened. 



6. In spite of high temperature and favourable nutrition-conditions, 

 the larval stage may vary between + 5 and ± 18 months. It is possible 

 that hereditary factors may play a part in this. 



The number of moults varies greatly. 



II. The Pupa. 



7. The male and the female pupae are easy to recognise by a differ- 

 ence of morphological characters. 



8. The sex ratio, determined on a large number of individuals, may 

 be taken as equal. 



9. The difference in dimension between the male and the female 

 pupa is small; the sexual ratio amounts only to 1'007 if the female is 

 taken as unity. The coefficient of variability is for the males higher 

 than for the females {^ v = 12-52 ; %v = 11-50). 



III. The Beetle. 



10. The size of the beetle varies between 10'5 and 23*5 millimeters. 



