HARDWICKE'S SCIENCE-GOSSIP. 



35 



therefore much increased in size, but not so limpidly 

 transparent as the (empty ?) space surrounding the 

 annulus externally. Immediately within the annulus, 

 on the morning of the 7th, I observed the clear area 

 all round to the peduncle or umbilicus on both sides, 

 to have its outer edge crenated. In the more advanced 

 eggs these crenations soon developed into a row of 

 (ventral) segments, twelve in number, marked off from 

 the rest of the central area by a curved concentric line. 

 These segments had an optical area from four to six 

 times as large as the reticulations of the chorion (say 

 about 555 inch in diameter). Soon three of them, 

 at the south extremity of the series, appeared larger 

 than the rest and furnished with processes sloping 

 northward ; whilst still further to the south, but less 

 distinctly, two or three other segments could be made 

 out having also processes sloping in the opposite 

 direction. Into this space, corresponding to the 

 region between the head and the body, faint cloudlets 

 of yolk-granules appeared as it were passing in from 

 the annulus towards the central area. Owing 

 probably to the sloping in opposite directions of the 

 thoracic and cephalic processes, there was lesspressure 

 here of the amnion against the serous membrane and 

 freer passage for the yolk. This appearance at this 

 region was visible persistently. in all'the eggs (Fig. 34). 

 The thoracic processes or legs were about half the 

 width of the segments from the posterior Jialf of which 

 they took their origin, but considerably longer, 

 passing out of sight in the annulus (Fig. 34). About 

 this time I noticed also other appearances as of 

 curved concentric lines marking out a tube 

 (mesenteron ?) but which would require further 

 observation for their certain interpretation. Upon the 

 same day (Aug. 7) in the afternoon, I noticed eye 

 spots (in all but N.W.) a group of about six arranged 

 in a circular form (Fig. 35). There were now visible at 

 least four cephalic segments, and it was at the base 

 of the third (reckoning from behind forwards) that 

 the group of eye-spots was situated. Later on I saw 

 a fifth larger terminal mass forming the extreme 

 anterior extremity of the embryo. The thoracic legs 

 appeared to be jointed. At 2.50 P.M. I noticed that 

 the twelfth (ninth abdominal) segment was somewhat 

 longer than the others and projected inwards towards 

 the centre, beyond their level. At 6.55 p.m. this 

 inward projection had disappeared, and a very im- 

 portant change in the terminal segment had been 

 initiated. It had become ventrally incurved upon 

 itself (Fig. 36). This segment was elongated, and 

 narrowed at the apex. It advanced steadily forwards 

 along the ventral aspect of the embryo, followed by 

 the others, and growing larger at the same time ; but 

 the head remained always in its original place. On 

 the morning of the 8th the last three segments (10-12) 

 were round the corner (Fig. 37) ; at 9.10 a.m. the tail 

 was in contact with the metathoracic legs ; at 12.45 

 P.M. it had gone beyond the two posterior pairs of 

 legs, which, with the forelegs, were now directed 



forwards in place of backwards as at first. The 

 middle of the bend of the abdomen (at the incurvature) 

 was between the third and fourth abdominal segments ; 

 at 1 p.m. the tail had come quite up with the fore- 

 feet ; at 2.40 P.M. it reached fully up to the head and 

 fully filled the larger northern bay. At this time the 

 stump of the umbilicus on the one hand, now reduced 

 to a mere conical point, and a similar projection from 

 the opposite side of the annulus, where cloudlets of 

 yolk-granules were passing in towards the neck 

 region (see Fig. 34), indicated a division of the whole 

 interior space into two unequal bays, of which the 

 smaller (southern) contained the head, and the other 

 the rest of the body. The second abdominal segment 

 might be said to form the keystone of the arch where 

 the abdomen was bent on itself, but the head, though 

 free in its bay, remained mostly in close contact 

 with the umbilical stalk. On the morning of the 9th 

 the tail reached quite to the level of the head and 

 beyond the eye-spots. The embryo lay in a loop 

 with the legs inside, a position which it had reached 

 by the growth and enlargement of the tail without any 

 change of place in the head and anterior segments. 



I have dwelt at some length on this incurvature 

 and growth of the tail by which the lepidopterous 

 embryo attains the loop-form in the shell, because 

 Kowalevski has stated (Mem. de l'Acad. Imp. des 

 Sciences de St. Petersbourg, vii. serie, tome xvi. 

 No. 12, p. 56), that it does so by the whole embryo 

 turning round in the shell after its tail. "Dem 

 Hinterende folgend, dreht sich der ganze Embryo so, 

 dass er jetzt der ihn noch bedeckenden serosen 

 Hiille den Rucken zuwendet, und die Extremitaten 

 erscheinen nach innen gerichtet." 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 yolk in the egg of 

 Gastrophysa raphani, e.g., turns always towards the 

 upper surface, though this change takes place so 

 slowly that it may occupy several days in comple- 

 tion. 2nd. Movements of growth ; strikingly illus- 

 trated in the egg of Calopteryx, in which the embryo 

 becomes inverted in the shell (v. Balfour, Comp. Em- 

 bryol. i. 334). 3rd. Embryonic movements ; by which 

 limbs or parts show movements without any change 

 of place in the whole ; and, lastly, larval movements ; 

 when the perfectly 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 lepidop- 

 terous embryo, Kowalevski supposes 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 embryo 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. 



