INSECTS 



389 



There is much variety in the details of the structure of these saws, 



so much, indeed, that it is possible to identify most of the species 



by means of the saw alone." The course of the life-history of a 



typical species, the Turnip Saw-Fly (Athalia spinarum, fig. 912), 



is as follows. The females lay their eggs during May in the edges 



of turnip leaves, or those of allied plants, cutting little slits for 



their reception. From 200 to 300 are deposited by a single 



turnip-fly. The egg increases in size after being laid, and the 



larva which hatches out in a few days closely resembles the cater- 



pillar of a butterfly or moth, in the possession of three pairs of 



jointed legs in front, corresponding to the legs of the perfect 



insect, and sucker - bearing 



pro-legs behind these. But 



the head is rounder and the 



pro-legs more numerous than 



in a true caterpillar. The 



young larva is pale in colour, 



but with increasing size be- ^ 



comes first green and later \^ x\ \, 



on blackish. The full-grown 



larva creeps down to the 



ground and enters the earth, f Fi f 9".-Tu P saw-Fiy (Athalia ,>,,,). , 



female, enlarged (natural size indicated to left of it); 2, 



Where it SpinS a Silken CO- enlarged and natural size; 4, 5, 6, larvae; 7, cocoon; 8, pupa in 

 i . , . t r cocoon. 



coon, to which particles of 



soil adhere externally. Within this shelter it passes into the 

 pupa stage, and the imago comes out about the end of July. 

 Under favourable conditions a second brood makes its appear- 

 ance the same year, and in this case the larva remains as such 

 within its cocoon during the winter, completing the stages in its 

 life-history the following May. 



Sharp (in The Cambridge Natural History) gives the follow- 

 ing intensely interesting account of another kind of Saw- Fly: 

 ''Although many kinds of Insects display the greatest solicitude 

 and ingenuity in providing proper receptacles for their eggs, and 

 in storing food for the young that will be produced, there are 

 extremely few that display any further interest in their descen- 

 dants; probably, indeed, the majority of Insects die before the 

 eggs are hatched, one generation never seeing the individuals 

 of another. It is therefore interesting to find that a fairly well 

 authenticated case of maternal attachment, such as we have 



A duu 



3, eggs, 



