ContrilniMon to the life Mstory of Onna tristis. 249 



Those of 0. tristis I watched during August two years 

 ago were well advanced when laid, none were so this year 

 till towards the end of August, so that it may be, that 

 only towards the end of its e^g-laying are the ova retained 

 until the larva is well-developed. But it is also certainly 

 the case that the ovum is not fertilised at the moment 

 of deposition, but at some interval previous to that time, 

 notwitbstandinor that the egg-shell is a solid structure 

 similar to that of eggs that have (as, in fact, these always 

 have) to exist externally for some time before hatching. 



They have, in fact, taken the first step towards becoming 

 viviparous, and it is of interest to note that the step is 

 not a definite and constant one, but varies from a habit 

 nearly that of ordinary egg-laying insects, to one that is 

 almost that of vivipaiity, not in ditferent races of the 

 beetle, or even in ditferent individuals, but apparently in 

 the same individual possibly according to its age. Not 

 certainly according to differences of treatment, as all my 

 beetles were kept together, yet their habits were not 

 always all alike. 



It is interesting to notice that Mr. W. M. Wheeler in the 

 Journal of Morphology (Boston), vol. iii., 1889, figures 

 the young larva of fJo^ryyho'ra clecemliineata as existing 

 within the egg-shell as almost identical in appearance with 

 that of 0. tristis. The only difference I note in his figure 

 or description is that the hatching spines in D. decernlineata 

 have definitely sharp apices, those of 0. tristis being com- 

 paratively flat and blunt. He describes the hatching as 

 taking place by the contained larva moving within the 

 egg-shell so as to cut it with these spines, and says that it 

 cuts the egg on both sides and that these two incisions 

 meet over the apex, making one large opening. I should 

 certainly like to see this process take place ; still I see no 

 reason to doubt that it is very possible for similar struc- 

 tures in allied species to exercise the same functions, or at 

 least to attain the same objects in verv' different ways. A 

 remarkable instance of this I mentioned lately to the 

 Entomological Society in the case of two species of Lepi- 

 doptera, Hyhocorupa milhausiri and IT. dryimypa, in which 

 a similar pupal spine is used in quite a different way in 

 each species for opening the cocoon. 



In 0. tristis it is certainly the case that no movement of 

 the young larva takes place before the opening in the egg 

 is formed, and that it takes place by rupture under tension 



