148 INSECT TRANSFORMATION 



whose larvae have the nervous system concentrated like that 

 of the blow-fly maggot, but which in the adult state possess 

 from two to five distinct abdominal ganglia though the thoracic 

 nerve-centres are all combined. Certain members of the family 

 Stratiomyidae, and of the Syrphidae : the wasp-like Volucellae 1 

 for example, afford examples of this curious modification in 

 which it is clear that the nervous system of the larva has 

 undergone a greater specialization from the primitive seg- 

 mented type than has that of the imago. A feature common 

 to all these transformations of the nervous system is the rapid 

 growth of the brain both in size and complexity during the 

 early pupal period, so as to bring about the correlation of that 

 great nerve-centre with the highly organized head of the adult 

 with its elaborated sense-organs. 



Turning to the circulatory system, it appears that the heart, 

 a comparatively simple tubular organ in both larva and adult, 

 survives with modifications all the stages of the life-history, 2 

 continuing its rhythmical contractions during the pupal period. 

 Part of the pericardial tissue also persists from the larva to 

 the imago. 



The digestive system of a transforming insect undergoes 

 on the other hand an extensive process of destruction and 

 rebuilding, especially in cases where the manner of feeding 

 of the larva differs markedly from that of the adult. Attention 

 has already been drawn, for example, to the striking contrast 

 between the food-canal in caterpillar and butterfly (pp. 59-60, 

 Fig. 30), adapted respectively to the digestion of solid and 

 liquid food. The lining of the larval stomach undergoes 

 degeneration and the cells are shed into the cavity, while from 

 small deeply-situated replacing cells the more delicate lining 

 of the adult stomach is developed. This process has been 

 lately studied in the development of bees and wasps 3 in whose 

 grubs the replacing cells can be already distinguished in sections 

 through the stomach taken at an early larval stage (Fig. 85) . It 

 has been previously mentioned that the greater portion of 



1 J. Kiinckel d'Herculais : " RScherches sur 1'organization et le 

 developpement des Volucelles ". Paris, 1882. 



2 A. Kowalevsky : " Die nachembryonale Entwicklung der Musciden ". 

 Zeitsch. f. wissensch, ZooL, XLV. 1887. 



8 J. Anglas : " Observations sur les Metamorphoses internes de la Guepe 

 et de la 1'Abeille." Bull. Sci. France et Belg., XXXIV. 1901. 



