OF THE GLOWWORM (lAMPYKIS NOCTILUCa). 51 



this insect : I had noticed only that the egg had considerably- 

 increased in size, but had not in any way changed its coloiu'. It 

 however, appeared now to be slightly effulgent on the day before 

 the young appeared, — a phaenomenon which I subsequently found 

 to be attributable to the embryo within. I saw one specimen 

 immediately after leaving the ovum : at first it was coiled up and 

 inactive, — a circumstance which I attribute to its being still 

 enclosed in the amnion after the shell has burst. It was then of 

 a very delicate straw-white colour, and for a few minutes quite 

 inactive : as soon, however, as its body is stretched out and the 

 amnion removed, it begins to move very feebly, but after a short 

 time with more strength. Its coloiu* also begins to change, the 

 white becoming of a darker shade, and in less than half an hour 

 the whole body is tinged of a very light grey. In the course of 

 two or three hoiu-s this colour becomes much darker, and after 

 some hours longer it is of a dull black, like the body of the parent. 

 Its body is then composed of thirteen segments, including the 

 head, and it moves with considerable activity ; its onward motion 

 being mainly effected by means of the anal segment, which serves 

 the purpose of the prolegs of herbivorous larvae in assisting the 

 progi'ess of its body. 



The length of time which these eggs had occupied in development 

 was thus on the average about forty-five days, or a little more 

 than six weeks. The other specimens, which had remained in the 

 box attached to the roots of grass, were hatched in about the same 

 time ; but the period of incubation was shorter by ten or twelve 

 days than that occupied in the development of a brood of glow- 

 worms' eggs in the preceding year, when the temperature of the 

 season was very much lower with rain. 



During the time the specimens above referred to were in course 

 of development, the heat was above the average, for at the latter 

 part of the time on one day it was 86°, and on more than one it 

 ranged from 76° to 78° Tahr. This result agrees with that derived 

 from the observations I have before and since made, viz. that the 

 more or less rapid development of the embryo is mainly dependent 

 on difierences in the amoixut of heat supplied to it from without. 



The Food and Habits of the Larva. 



Six days after the larvae were hatched, I supplied them with their 

 proper food — a portion of a living snail, which they immediately 

 began to devour with great avidity. Before this they had sipped 



4* 



