lejndopteroKs lariuc and jwpcB. 



163 



horizon. The number of ova seems to be smaller upon 

 smaller larvae. Thus, in ' Entomologist,' xvi., p. 69, 

 only two eggs are described as occurring upon the larva 

 of \lcrontjcta psi: Newport describes eight eggs of P. 

 iestaceas upon TI. jiisi. It is probable that an excess of 

 ova are generally laid, for a small proportion do not 

 develop, and the way in which they are attached in 

 small groups ensures that of those that do develop a 

 large proportion of the larvae are so crowded by the 

 others that they die at an early stage, as has been also 

 previously observed. If too large a number were laid 

 and all developed it is obvious that none could arrive at 

 maturity, but this is obviated in the manner described 

 above, and it is partly brought about by the limited 

 space on the circumference of the larva attacked. This 

 space of course varies with the size of the latter, and it 

 is more quickly filled in the rapid development of the 

 parasites upon" small than upon large larvae, so that, if 

 they are too numerous, crowding ensues earlier, and 

 with more fatal results in the former than in the latter 

 case. Thus the smaller surface may compensate lor 

 the less amount of food, and may itself ensure that the 

 parasites reach maturity. 



The following figures support the conclusions advanced 

 above, that the ichneumon lays a smaller number of 

 eggs on small larvaj than it lays upon large ones, and 

 yet lays more than can develop in nearly all cases, the 

 eggs being laid in such a way that crowding results if 

 all, or nearly all, develop ; so that the chance of the 

 eggs being sterile is obviated on the one hand, and of 

 the parasitic larvae dying immature on the other. On 

 I), vinula I found fourteen eggs, of which seven became 

 mature, and an equal number of eggs, which I did not 

 allow to develop, on another larva of the same species. 

 DeGeer speaks of " more than eight or ten eggs " on the 

 same species of larva, and describes nine ichneumons 

 emerging in another case, and six larvae _ becoming 

 mature in another, while Gocdart speaks of five. Of 

 Newport's eight eggs on 11. pisi three became mature 

 (but died), while in several cocoons of this larva he 

 found two to three cocoons of the parasite, and four m 

 one instance, when the parasites were dwarfed. In many 

 of the above instances the writers show that the larvae de- 

 veloped in groups, thus tending towards overcrowding. 



