GENERAL CONSIDERATIONS. 387 



thought) take any direct share in the building up of the tissue. 

 Their significance seems to be that of destroyers of the larval organs 

 which are doomed to destruction; the constituent parts of these 

 organs are taken in and digested by them, and, through their 

 capacity of locomotion, they conduct particles of nourishment to the 

 organs that are in process of reconstruction. But what is the fate 

 of these elements after the ontogenetic processes in the pupa are 

 completed 1 There can be no doubt that some of the so-called 

 granular cells develop into ordinary blood-corpuscles. The majority 

 of them apparently undergo degeneration. The phagocytes them- 

 selves are finally used as food for the newly -formed tissues. Interest 

 attaches here to the observation of Van Rees that many phagocytes 

 finally wander into the newly-formed hypodermis, and there, in the 

 •spaces between the hypodermal cells, undergo degeneration. 



General considerations regarding the development of the 

 Imago in the Pupa. 



We have seen that the development of the body of the imago 

 proceeds from distinct formative centres (imaginal discs) already 

 present in the larva, having appeared during embryonic life. We 

 have met with such imaginal discs in connection with the different 

 parts of the head, the limbs, the hypodermis, and the various parts 

 of the intestinal canal. We have seen that the development of the 

 mesodermal organs of the imago (muscles, connective tissue, fat-body) 

 proceeds from a mesodermal part of the imaginal discs, the first 

 origin of which, however, is still somewhat obscure. Simultaneously 

 with the building up of the imaginal organs, we have the destruction 

 of the larval organs through the action of the phagocytes. These 

 two processes (disintegration and regeneration) go on side by side in 

 such a way that the continuity of the organ is in most cases perfectly 

 preserved, complete disintegration of the larval tissue only occurring 

 after the development of the permanent organ. The musculature of 

 the larva here forms an exception, as it undergoes disintegration very 

 early. 



We must, in conclusion, once more point out that the sharp 

 distinction between the larval, the pupal, and the imaginal stages 

 seems to be founded only upon the appearance of the external 

 surface of the body, as resulting from the consecutive moults. The 

 phenomena of internal development, on the contrary, represent a 

 complete, continuous series of transformations, which do not show 



