DEVELOPEMENT OF THE GRUB. 177 



campa Neustria) deposits her eggs in a spiral coil round the 

 stems of fruit trees (fig. 8). 



The period which elapses between the deposition of the 

 egg and the birth of the larva depends upon the temperature 

 of the atmosphere, as well as upon the species of the insect. 

 Thus, whilst the early-laid eggs of the tortoise-shell butterfly 

 hatch in a few days, those which are not laid till autumn 

 will not produce caterpillars until spring. The eggs of the 

 meatfly hatch in a very few days, or even hours : eight days 

 are required by the eggs of the painted-lady butterfly ; whilst 

 the caterpillars of the machaon butterfly are not hatched un- 

 der a month. It is, however, a general rule, that those eggs 

 which are deposited in the autumn are not hatched until the 

 following spring. 



The investigation of the developement of the grub whilst 

 inclosed within the egg is attended with so much difficulty, 

 owing to the minuteness of the objects, that hitherto but lit- 

 tle progress has been made in this branch of the subject. Dr. 

 Herold, however, whose admirable microscopic observations 

 1 have already noticed, has taken it up ; and the first part 

 of his magnificent work, intitled " Disquisitiones Animalium 

 Vertebris carentibus in Ovo Formatione," has recently ap- 

 peared, and will tend to throw much light upon this intricate 

 subject. One peculiarity ought not to be omitted relative to 

 this part of our subject, namely, that the eggs of the sawflies, 

 gallflies, and ants, increase very considerably in their size 

 and alter in form previous to the exclusion of the larva, 

 which is doubtless owing to the membranous covering of the 

 egg and to the growth of the inclosed larvae. In general, 

 the embryo caterpillar is observed coiled up within the egg, 

 the head being brought into contact with the tail. 



We have said that the majority of insects die previous to 

 the birth of their progeny, but this is not the case with the 

 whole. Thus De Geer ascertained that a large species of 



