O. A. Mbrritt Hawkbs 137 



definite. The drawing on Plate V (8), which is not sufficiently clear to 

 be authoritative, shows no spots. 



The difference between the two species therefore is, that whilst 

 cynthia has seven complete series of black spots, five of these are entirely 

 lacking in ricini and the remaining two are generally partially present 

 but are variable. The condition in cynthia is therefore called spotted 

 and denoted by S, whereas that in ricini, which superficially looks plain, 

 in spite of the lower lateral series, is called plain and is represented by 

 P. (Plate VIII, figures B 2, C 3, C 4.) 



Method of Rearing. 



The larvae were reared at first in glass-lidded boxes, and later in 

 zinc cages covered with black net. The room used for breeding pur- 

 poses was heated by steam pipes and kept damp by water boxes on the 

 pipes and damp cloths over the open cages. The minimum of handling 

 was resorted to — I soon dropped the usual method of moving the young 

 larvae by means of a camel's hair brush, as it seemed unsuitable to a 

 larva so well provided with setae, preferring the more .tedious method of 

 waiting until the larvae had crawled on to a leaf or stem which could 

 be moved by forceps. The greatest care was taken to keep the boxes 

 clean ; when changed they were sterilised with boiling water and in the 

 later stages, when disease appeared, by boiling water plus carbolic. 

 Periodically the larvae were all turned out of the room and the room 

 was sterilised with a formalin apparatus, but as the experiment and the 

 War progressed coincidentally, it became impossible to obtain the 

 formalin and finally, after nearly two years, there was much disease. 

 The larvae were doubtless very susceptible to disease as, owing to 

 inadequate warmth, they were eating little and growing slowly. 



Cynthia and ricini were crossed by Mr J. W. Watson at Manchester. 

 He divided the eggs between a number of entomologists, giving me 

 180 eggs from which 149 adult larvae were reared. Unfortunately, the 

 other breeders reared only a very small proportion of their larvae and 

 kept no record of the characteristics. 



The Fi generation. 



All the 149 larvae of this generation had spots on the upper part 

 of the body ; most had the full complement of spots characteristic of 

 cynthia and were therefore spotted (S), but some had only a portion of 



10—2 



