THE society's NOTE-BOOKS. 



55 



figure ; and, having soaked the portion thus cut off in liquor 

 pottasscB and well washed it, we then view it from within in a 

 little water, we shall, I think, see something like Fig. ii, where 

 5 d. and 5 v. are the edges of the Y\^. ii. 



dorsal and ventral plates of the fifth 

 segment ; 6 d. and 6 v. those of the 

 sixth segment. Thus far is plain 

 enough, and it is noticeable how the 

 dorsal arches overlap the ventral. 

 Within these are the sexual seg- 

 ments, which are more difficult to 

 follow. The first in order is that 

 which I have marked 7 d.^ and it is 

 not difficult to recognise this as the 

 seventh dorsal plate, forming as it 

 does a distinctly continuous arch on the dorsal side, and not 

 extending round to the ventral. Although, as I have said, dis- 

 tinctly continuous on the dorsum, this plate is nevertheless very 

 narrow here, and attains its greatest breadth onj each side, 

 where a pair of spiracles are situated, below which is a suture, ss, 

 (see Fig. 12), and then again another Fie. 



small triangular piece on each side, 

 concerning which I am doubtful whether 

 or not it is a portion of the correspond- 

 ing ventral arch, but in either case the 

 ventral arch of this segment cannot be 

 traced all round. 



I have called attention to the nar- 

 rowness of this plate in the dorsal region because I believe 

 it indicates a transition, which is further exemplified in the 

 two succeeding segments, by considering which we shall 

 perhaps better understand them, for in the next or eighth seg- 

 ment we find the dorsal arch (marked 8d.^ Fig. 11), thinned 

 away on its dorsal surface to a fine line, and even this vanishes 

 quite away in the centre, while its lateral parts are considerably 

 broadened and prolonged round towards the venter, so that 

 it is difficult to say whether this plate is dorsal or ventral. In 

 the last or ninth segment (marked Q d., Fig. 11), the continuity 

 of the dorsal plate on its dorsal aspect is altogether lost, while its 

 lateral portions are so developed towards the venter (forming as 

 they do the basal portions of the sheaths of the sting), that they 

 might, unless carefully looked at, be mistaken for a ventral plate, for 

 which, indeed, I at first mistook them. For the reasons mentioned, 

 however, I regard these three plates as all dorsal. The dart 

 evidently connects the ventral portions of the sheaths, and on this 

 account I regard it as the ventral plate of the ninth segment \ it 



