148 



thelial disks of the pre-rectal ampulla. It may be pointed out 

 that this theory of larval respiration rests on anatomical and 

 histological data, not on physiological experiments. 



Sadones also called attention to the lack of correspondence 

 in position between the rows of gill-plates of the rectum and the 

 so-called rectal glands, as the latter alternate with the former, 

 and to the bearing of this fact on the homologies of the rectal 

 glands in insects generally. 



Calvert (1911) has discovered well-developed, paired, ventral, 

 tracheal gills on a number of the abdominal segments of the 

 larva of the Costa Rican Cora, one of the Calopteryginae, struc- 

 tures hitherto known only on a couple of Old World (Indian) 

 genera of the same subfamily. The presence of such organs 

 naturally suggests a very primitive condition and a point of 

 contact with the larvae of Ephemeridae and Sialidse. 



Needham (1897) traced the changes which occur in the 

 epithelium of the stomach or mid-gut of larvae during fasting 

 and after feeding, finding in the latter case that the most turgid 

 ceUs, containing presumably digestive ferments, are bodily dis- 

 charged into the lumen to mix with the food and are replaced 

 by other previously smaller cells. His results were confirmed 

 and extended by VoiNOV in the following year (1898), who 

 showed that, previous to the actual detachment of whole cells 

 into the lumen, clear or coloured liquids may be secreted from 

 them. By mixing colouring matters with the food, Voinov 

 ascertained that the same cells w^hich secrete these liquids also 

 absorb material from the lumen at the same time. He traced 

 methylene blue absorbed in this way into the body cavity and 

 thence into many other organs, e.g. the developing ovaries. 

 Other colouring matters, such as cochineal, introduced into the 

 alimentary canal, were not absorbed, showing a selective absorp- 

 tivity on the part of the intestinal epithelium. He also obtained 

 evidence of absorption in the opposite direction, for, on injecting 

 congo red in physiological salt solution into the body-cavity, 

 granulations of this dye-stufí were found not only in the peri- 

 cardial ceUs, but also in the peritrophic sac of the mid-gut lumen. 

 Eosin, similarly injected into the body-cavity, appeared in the 

 Malpighian tubes and in the mid-gut lumen. Only in the mid- 

 . gut was there evidence of the absorption of fats and other 



