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 {Aikalia 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 litde slits for 

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

 turnip-fly. The &g<y 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 N ^ ^ "~x-\( \ \ '^. .. "^S>^ 

 on blackish. The full-erown 



larva 



creeps 



down to the 



ground and enters the earth, , '''f s-^.-Tumip saw-Fiy [Athaiu, si,iuaru,n). ,, Aduu 



o ' female, enlarged (natural size indicated to left of it); 2, 3, eggs, 



where it SOmS a silken CO- enlarged and natural size; 4, 5, 6, larvae; 7, cocoon; 8, pupa in 

 1 . , . , p cocoon. 



coon, to which particles oi 



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 T/ie 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 



