THE PRESIDENT'S ADDRESS. 385 



and thorax from itnaginal discs. He also traced these discs to 

 their origin, the larval tissues to which they correspond. 



Dewitz in 1878* showed that the process of development in the 

 Hymenoptera and Lepidoptera is not unlike that in the Diptera, so 

 that we must regard the imaginal discs as capsules of reserve, 

 developed in relation with the same embryonic structures which 

 they are destined to represent in the imago, or, as fragments of the 

 original blastoderm to be nourished by a new yelk, formed by the 

 disintegration of the larval tissues. 



The manner in which this disintegration is brought about has 

 been the subject of careful investigation, and in this relation I must 

 again refer to the excellent work of Dr. Viallanes. The record of 

 this work will be found in Vol. xiv. of the 6th series of the 

 " Ann. Sc. Nat. Zool.," published in 1882. Nearly the whole 

 volume is occupied by his elaborate paper. Dr. Viallanes has 

 there recorded a vast number of facts connected with the develop- 

 ment, structure, and disintegration of the larval tissues. He calls 

 this process of disintegration " histolysis " ; he also did much to 

 elucidate the manner in which the new tissues of the imago are 

 developed. With regard to the true nature of this histolysis, by ' 

 which a new nutrient yelk originates in the pupa, Viallane's 

 observations apparently led him from the main process, which 

 he did not discover. 



D. Barfurth in 1882f investigated the process of absorption 

 which occurs in the tail of the tadpole, and discovered that the 

 tissues are invaded by protoplasmic amoeboid cells, white blood 

 corpuscles or lymph corpuscles, and that these, which he terms 

 phagocytes, are the main agents in their disintegration. That 

 such processes occur in the development of bone had long been 

 known, and that phagocytes are important agents in morbid pro- 

 cesses has long been suspected. In 1883 Metschnikoff published 

 a paper on this subject, and within the last few months Kowalevski? 

 of Odessa, one of the most successful and brilliant living biologists, 

 has published an extensive series of investigations on the after- 

 development of the blow-fly, in which he clearly shows that the 

 disintegration of the larval tissues is mainly due to their invasion 

 by phagocytes.J 



* " Zeits. f. w. Zool.," Bd. xxx., Sup. 

 f " Archiv. f. Mic. Anat.," Bd. xxix 

 j " Zeits. f. w. Zool.,' Bd. xlv. 



Journ. Q. M. C, Series II., No. 24. 29 



