THE HIDDEN TYPE OF WING-GROWTH 147 



certain members of the gall-midge family (Cecidomyidae), 

 larvae might contain within their bodies small live larvae 

 which ultimately made their way out through the skin and 

 cuticle of their precocious parent, and later it was seen 1 that 

 these offspring arise from eggs, which breaking loose from the 

 early-developed ovaries, float about in the body-cavity where 

 they undergo segmentation and growth. After several of 

 these abnormal generations the larvae are stated to pupate 

 and develop into male and female midges. Such power of 

 reproduction by immature creatures (paedogenesis) though 

 very remarkable and interesting, is not unknown among other 

 groups of animals, in some cases as a normal phase in the 

 life-history. 



The central nervous system commonly passes like the 

 reproductive organs from the larval through the pupal to the 

 perfect stage by a gradual process of growth and change without 

 sudden and critical transformation or re-making. 2 From the 

 brief account already given (ch. ii, pp. 56, 60) of the nervous 

 system of a butterfly as compared with that of its caterpillar, 

 it may be inferred that the three thoracic ganglia, spaced from 

 one another in the larva become closely approximated in the 

 imago, while the number of abdominal ganglia becomes reduced 

 through the coalescence of the hinder two or three. Such 

 concentration in the adult as compared with the larva is shown 

 still more markedly in the case of a bee, whose grub has three 

 distinct thoracic and eight abdominal ganglia, while in the 

 winged insect the thoracic ganglia are closely coalesced and 

 there are only five abdominal. On the other hand there are 

 larvae, such as the maggot of a blue-bottle, in which, as already 

 mentioned (p. 136), all the nerve-centres behind the brain 

 are combined in a large mass lying below the gullet. In the 

 adult blue-bottle the same concentration is maintained, but the 

 ventral ganglion now lies in the thorax some distance behind 

 the brain and a median cord extends backwards into the 

 abdomen. It is particularly interesting to find some flies 



1 M. Ganin : " Neue Beobachtungen iiber die Fortpflanzung der viviparen 

 Dipterenlarven " . Zeitsch, f. wissensch Zool. XV. 1865. W. Kahle : 

 " Die Paedogenesis der Cecidomyiden " . Zoologica, IV. 1908. 



2 G. Newport : " On the Nervous System of the Sphinx ligustri ". Phil. 

 Trans. R. Soc. 1832-4. And " Insects ", in Todd's " Cyclopaedia of 

 Anatomy," Vol. II. 1839. 



