40 



PSYCHE. 



[March 1S91. 



phoses and their suitability to the num- 

 ber, variety, and novelty of the changes 

 in the surrounding's and the correspond- 

 ing changes in habits of the larvae at 

 different stages of growth. 



The occupation of the larval stages 

 by strange and curious forms, like cat- 

 erpillars, grubs, etc., naturally attracts 

 attention and at first makes one wonder 

 at the apparent eccentricities of nature's 

 ways. But in reality they serve to 

 throw a strong side light upon the nor- 

 mal mode of action of the laws of hered- 

 ity, and show us that, in spite of its 

 enormous conservative force, heredity 

 is subservient to the effects of habit or 

 use of parts. 



That these secondary larval forms are 

 more reduced, although more special- 

 ized organisms than the primitive Thy- 

 sanuriform larvae, has already been 

 stated. Among Coleoptera and Neu- 

 roptera this is obvious whenever the 

 Thysanuriform and secondary adaptive 

 forms are present in the growth of the 

 same individual. No one can compare 

 the swollen, soft, round-bodied grubs 

 with the active Thysanuriform larva, 

 especially when occurring in the growth 

 of the same beetle, without realizing 

 that the former is due to specialization 

 by reduction. That their structures, 

 although degraded by this process, are 

 suitable to the conditions under which 

 they live has been pointed out by many 

 writers ; notably, Graber, Riley, Lub- 

 bock, and Packard. This reduction 

 becomes still more apparent when we 

 regard the larvae of Diptera and the 

 grubs of the weevils among Coleoptera, 



the latter being generally without legs, 

 and the former also deficient in these 

 organs and in large part without a dif- 

 ferentiated head. If these or the cater- 

 pillars or other secondary larval forms 

 similar to them were isolated, and their 

 subsequent development into pupae 

 and adults unknown, naturalists would 

 no admit that they possessed close affin- 

 ities with the adult insects of the same 

 groups, and they would be considered 

 as more rudimentary or simpler in 

 structure than any Thysanuran or Thy • 

 sanuriform larva. In the most special- 

 ized forms of Coleoptera, the weevils, 

 the early development of a footless grub, 

 a reduced form similar to the maggot of 

 the Diptera, replaces both the Thysa- 

 nuriform larva and also the active six- 

 footed grub of the normal groups of 

 beetles. The Insecta furnish such ap- 

 parently isolated examples, and, on ac- 

 count of the absence of intermediate 

 forms, it has been supposed that these 

 could be put in evidence against the 

 derivation of the orders of which they 

 were members from Thysanura, as has 

 been stated above with reference to the 

 saltatorial Orthoptera, but the researches 

 of Brauer, Packard, and Lubbock, de- 

 monstrating that the secondary larval 

 stages, grubs, maggots, etc., are modi- 

 fications of the Thysanuriform larval 

 stages, show that this- use of them can- 

 not be admitted. If this be granted, it 

 becomes possible to account for the phe- 

 nomena as follows. The modified, and 

 adaptive, larval characters of the grubs, 

 caterpillars, etc., having become fixed 

 in the organization of such groups as 



