142 REGINALD G. HARRIS. 



M 223, and M 224. These pupa-larvae were transferred to fresh 

 cultures, made of the same stock culture medium, and maintained 

 under conditions as similar as possible to those of the control 

 cultures. On this occasion, however, pupa-larvae were separated 

 into two age-groups. 



It will be remembered that the spathula sternalis, a structure 

 characteristic of pupa-larvae in this material, is unpigmented 

 when the larvae are born, but becomes pigmented later, until, 

 about three or four days after the pupa-larvae is born, the 

 spathula sternalis is dark brown in color. Thus the presence or 

 absence of pigment in the spathula sternalis offers a rough index 

 of age. This index was employed. Pupa-larvae in which the 

 spathula sternalis was unpigmented were placed in one series of 

 fresh cultures, those in which pigmentation was clear were 

 placed in another series. Four such cultures were formed, 

 MPW 190, MPW 192, MPWO 191 and MPWO 193. The even 

 numbered cultures contained only pupa-larvae in which the 

 spathula sternalis was pigmented; while in the odd numbered 

 cultures none of the spathulae sternalis was pigmented at the 

 time of transfer. All larvae were, from a morphological stand- 

 point, typical. 16 pupa-larvae with spathula sternalis pigmented 

 were transferred to culture MPW 190; and 22 to culture MPW 

 192. Of the former, 7 metamorphosed into pupae, and later into 

 adults, while 9 produced young paedogenetically. In culture 

 MPW 7 192, of the 22 pupa-larvae present, 13 metamorphosed into 

 pupae and later into adults, while 9 gave rise to young paedo- 

 genetically. It is significant that in the cultures made from 

 younger pupa-larvae, as evidenced by the absence of pigmentation 

 in the spathula sternalis when the larvae were transferred, of the 

 15 pupa-larvae in culture MP\VO 191 only I metamorphosed into 

 a pupa, and later into an adult, while 14 produced young paedo- 

 genetically. In culture MPWO 193, of the 8 pupa-larvae present, 

 none continued their development in the manner characteristic 

 of pupa-larvae, but all showed a reversal of function, giving rise to 

 young in the manner of typical paedogenetic larvae, though in 

 most cases the number of young born was less than that of 

 paedogenetic mothers from the same stock. All the young which 

 were produced by the pupa-larvae-mothers were, morphologically 

 and functionally, typical paedogenetic larvae. 



