I4O REGINALD G. HARRIS. 



have been examined, none have been noted, either in nature or 

 in the laboratory, in which the morphological appearance of the 

 two larval forms did not correlate perfectly with the function of 

 the larva, under normal conditions. Thus the writer and other 

 observers have used the terms pupa-larvae, and paedogenetic 

 larva? as definite terms (Springer '17, Harris '23, '24), based upon 

 visible morphological differences, corresponding absolutely to 

 functional differences. Paedogenetic larvae consistently give 

 rise, by paedogenesis, to other larvae; whereas pupa-larvae never 

 give rise directly to other larvae, under normal conditions, but 

 continue their development by metamorphosis. 



Recently I have indicated, as the result of a series of experi- 

 ments, that pupa-larvae may be obtained at will in the laboratory 

 by crowding in the previous generation (Harris, '23, '24). 

 During these studies, counts were made of pupa-larvae which had 

 arisen from crowded cultures of paedogenetic larvae. It was 

 found necessary, in order to make accurate counts to remove the 

 pupa-larvae from the original culture to a fresh culture, at the 

 time of counting. This procedure removed the possibility of 

 counting the same larva twice, and, at the same time, permitted 

 counts to be made as pupa-larvae arose in the culture; thereby 

 making the larvae available for other experiments. 



Upon examining the abdominal contents of pupa-larvae which 

 had been transferred to fresh cultures, I observed in one pupa- 

 larvae not only eggs but young embryos. Both the eggs and 

 young embryos were clearly distinguishable in the method 

 employed. 



Pupa-larvae were placed in Ringer's solution on a slide and the 

 anterior portion of the pupa-larvae was removed with dissecting 

 needles. The contents of the abdominal cavity were then 

 forced out through the opening thus made; the larval skin was 

 removed and the material was stained with a modified aceto- 

 carmine preparation. 1 



The pupa-larvae, already mentioned, appeared originally in 

 culture M 187, which had previously been subjected to intense 

 crowding. It, with other pupa-larvae, was transferred to a fresh 

 culture, MP 142, on December 30, 1923. \Yhen examined, as 



1 Acknowledgment is made for this staining method to Dr. Belling, of the 

 Carnegie Institution of Washington, who has employed it with success in cytological 

 work on Datura. 



