THE LIFE-HISTORY Of A LEPlDOPTEROUS INSECT. 241 



I'lie Life-jiistory of a Lepidopterous Irisect, 



Comprising some account of its Morphology and Physiology. 

 By J W. TUTT, F.E.S. 



(Continued from page 217). 



Chap. IV. 

 EMBEYOLOGY. 



12. — Eeversal OF POSITION OF EMBRYO IN EGGS. — (Continued). — 

 With regard to the development of the embryo in the egg of Rmnia 

 lateolata (crafacgata) and the position of its head in the ovum, Dr. 

 Osborne writes (E. M. 3L, vol. xx., p. 147) : — " The earliest eggs were 

 laid on or about the 15th of June. On the 28th I noticed the first 

 appeai'ance of the e3^e- spots, and the first hatching took place on 2nd 

 July. My note on 30th June runs as follows: — 'The eye-sjwts from 

 their earliest api^earance occupy the same position relatively to the 

 sharjD end of the polar oval as they do in these advanced embryos (and 

 which is their position up till hatching) : consequently the aspect and 

 orientation of the dorsal and ventral surfaces is constantly the same.' 

 That is, unless the embryo makes, more than four days before hatching, 

 that revolution in the shell asserted by Kowalevski for the lepidoj^terous 

 embryo in general, and which would necessarily bring its head from 

 one side of the shell to the other. The presumption then would be that 

 the embryo of R. crataegata gets into the loop form by such a ventral 

 incurvature and forward growth of the tail-end, as Ave have seen already 

 in Zavaea, and as is described by Huxley in Astaciisy 



To this (in Science Gossip, vol. xxi.) Dr. Osborne adds : — " Perhaps 

 the subject may be made clearer by a brief consideration of the 

 different kinds of motion which may be observed in eggs. These may 

 be classed under four heads ; 1st, Movements due to gravitation. The 

 ventral or developing side of the yelk in the egg of Gastrophi/sa 

 raphina, e.g. turns always towards the upjDer surface, though this 

 change takes j^lace so slowly that it may occuj)y several days in 

 completion. 2nd, Movements of growth : strikingly illustrated in the 

 egg of Calopteryx, in which the embiyo becomes inverted in the shell 

 (Balfour, Comp. EmhryoL, i., 334). 3rd, Embryonic movements ; by 

 which limbs or parts show movements without any change in the 

 whole ; and lastly, 4th, Larval movements ; when the jjerfectly formed 

 embryo changes its position in the shell or acts in any other way as if 

 it were independent of it. The loop form of the lepidopterous em- 

 bryo Kowalevski sujiposed to be due to the latter class of movements, 

 whilst in reality it is only a movement of growth. When in its final 

 stages, as stated by Kowalevski and as observed in these eggs by 

 Mr. Jeffrey, the embiyo of Botys devours the remainder of the yolk 

 and cuts its way out of the shell, these actions may be fairly described 

 as larval movements." 



As there was here a decided discrepancy between Dr. Osborne's and 

 Kowalevski's observations, and as my OAvn yiews agreed with tliose of 

 Dr. Osborne, viz. that the change in 2iosition Avas due to the groAvth of the 

 embryo pushing up the anal segment Ijetween tlie A^enter (placed out- 

 side) and the sliell avuU, tlie body being gradually pushed back into the 



