382 



INSECT A. 



Fig. ISO.— Larval digestive tract of one of the 

 Muscidae with the imaginal discs depicted (after 

 Kowalevsky). hd, caecal tubes of the chyliflc 

 stomach ; ch, chyliflc stomach ; /, fat-cells at 

 the apex of the salivary glands ; h, proctodaeal 

 imaginal [ring ; ht, proctodaeum ; ie, imaginal 

 cells of the mid-gut epithelium ; im, imaginal 

 cells of the muscles of the mid-gut; ims, pos- 

 terior abdominal imaginal disc ; is, imaginal 

 rings of the salivary glands ; ma, Malpighian 

 vessel ; pr, proventriculus ; s, sucking stomach ; 

 sp, salivary glands; v, stomodaeal imaginal 

 ring. 



Van Rees and Kowalevsky 

 are in entire agreement with regard 

 to the details of the disintegration 

 o'f the larval muscles by phagocytes, 

 which had already been the subject 

 of conjecture to Metschnikoff 

 and Ganin. According to Van 

 Rees, not all the muscles of the 

 larva undergo such disintegration. 

 Certain dorsal groups of the ex- 

 ternal oblique muscle of the second 

 thoracic segment are retained and 

 pass over into the wing-muscles of 

 the adult after radical internal 

 modifications consisting of an in- 

 crease in the number of the nuclei 

 and a rearrangement of the muscle- 

 substance". This manner of tran- 

 sition from larval to imaginal 

 musculature appears very remark- 

 able, but the descriptions of Van 

 Kees leave hardly any doubt as to 

 the accuracy of these observations.* 



As a rule, the formation 

 of the imaginal muscle-groups 

 takes place from the permanent 

 mesoderm, which is derived 

 from that of the imaginal 

 discs (Fig. 188 C, m). We 

 have already stated (pp. 375— 

 381) all that is as yet 

 known as to the origin of 

 the former. 



Intestinal Canal. 



The disintegration of the 

 larval intestine and the de- 

 velopment of the permanent 



* [According to recent investiga- 

 tions by Kawawaiew(No. XXIV.), 

 phagocytosis plays a very unim- 

 portant role in the metamorphosis 

 of Lasius, this being especially 

 noticeable in the disintegration of 

 the larval muscles; the phagocytes 

 here do not cause the liquefaction 

 of the fibres, but are only concerned 

 in the absorption of the liquid 

 mass. — Ed.1 



