109 



The Inheritance of Colour in the Stick-Insect, Carausius morosus. 

 By E. W. MacBkide, F.K.S., and Miss A. Jacksox. 



(Eeceived June 1, 1915.) 



[Plates 4 and 5.] 



The stick-insect, Carausius {Bixippus) morosus, is an inhabitant of 

 Southern India. The genus Carausius is closely allied to the genus Dixippus, 

 from which the principal feature which separates it is a keeled sternum on 

 the mesothoracic segment in Carausius, and the absence of such a keel in 

 Bixippus. In Carausius morosus this keel is obscure, and TVattenwyl and 

 Bedtenbacher (1908), whose classification we follow, include this species in 

 the genus Carausius on general grounds. Other authors have assigned the 

 species to Bixippus, whence it comes that in the literature the species is 

 frequently referred to as Dixippus morosus. 



It has been known for some time that this insect exhibited marked colour 

 varieties, and it occurred to us that it would be an interesting research to 

 determine the laws governing the inheritance of these variations. Our 

 material consisted of a batch of eggs received from India in 1911. A 

 preliminary research by the senior author in 1912 yielded such curious 

 results that it was determined to take up the investigation in detail, and to 

 this subject the junior author has devoted the last two years. 



Before detailing the results at which we have arrived, it will be desirable 

 to give an outline of our previous knowledge of the subject. The life-history, 

 habits, and principal colour variations of Carausius morosus were dealt with 

 in a paper by Meissner (1909), who received a batch of 300 larvae which had 

 just hatched, and reared them until maturity was attained. It is almost 

 certain, however, that in supposing his larva? to be just hatched Meissner 

 was mistaken, and that in reality they had completed their first moult when 

 he received them, for he asserts that egg-laying begins after six moults, 

 whereas according to our observations seven moults are passed through 

 before sexual maturity is attained. 



All his specimens were green when he received them, but out of -11 adult.s 

 successfully reared 17 were green and 2-1 brown. He states that when the 

 brown insects are kept in the dark between the fourth and fifth moult the 

 darkness of their colour becomes intensified. 



De Sinety, in a paper dealing with the biology and anatomy of the* 

 Phasmicke (1901), includes Carausius morosus amongst the species he investi- 

 gated. He reared both males and females, and commits himself to the 



VOL. LXXXLX. — B. — ■ K 



