16 MR. J. LUBBOCK ON THE DEVELOPMENT OF 
The basal segments have changed again in the manner already described, so that the 
strongest circles of spines are those on the third, fifth, seventh, eleventh, fifteenth, 
nineteenth, twenty-third, and twenty-seventh, in addition to which, that on the thirty- 
first segment has also distinguished itself by an increased development; so that the four 
darkest segments, which, until now, have immediately followed the last of these fourfold 
sections, now constitute the last quartet. 
This division of the central part of the tails into well-marked divisions, consisting of 
four segments each, is to my mind a very curious phenomenon. When the sixth and 
seventh segments divide, the old circle round the apex of the sixth, which is at first more 
conspicuous than the corresponding circles of the two new segments, tones itself down, 
until the three closely resemble one another ; on the other hand, the apical circle on the 
segment which in the last stage was the seventh resembles that of the surrounding 
segments. It, on the contrary, in accordance with some mysterious law, has become 
more conspicuous; so that the subdivision of the organ into sections of four segments 
is effected partly, and indeed principally, by the mode of growth, but partly also by the 
modification, sometimes by diminution, sometimes by development, of the apical circles 
belonging to old segments. 
The thirteenth state lasts for about a week, during which time the insect adds about 
sooths to its length. 
Fourteenth State. 
The rudiments of the wings now cover five-sixths of the metathorax. The antennz 
are still of about the same length as the body. 
The secondary plates have increased considerably in size on the five intermediate pairs 
of branchiz, but the first and last pairs have hitherto remained simple; now, however, 
the former show at their base a small thumb-shaped lobe (fig. 22). 
The lateral tails have grown as before: the last division of four, which is also the 
darkened portion, includes the thirty-second and three following segments; the fringe 
extends to the forty-third, beyond which there were at least seven more segments. 
The central tail now closely resembles the two lateral ones; it is, however, fringed on 
both sides, while the lateral tails have on their outer margin only the usual small hairs 
at the apex of each segment. There were twelve segments beyond the fringe. 
Fifteenth State (fig. 14). 
This stage commences when the insect has a length of about 1i3ths to 129ths, and the 
rudimentary wings reach to the end of the metathorax. 
The secondary lobe of the anterior branchize reaches almost halfway up the large plate. 
The more developed circles are now on the third, fifth, seventh, ninth, thirteenth, 
seventeenth, twenty-first, twenty-fifth, twenty-ninth, thirty-third, and thirty-seventh 
segments. The thirtieth and nine following segments are darkened, and the fringe 
extends to the fifty-first segment. The terminal segments were nine in number, though 
the organ was imperfect. 
In this case it would seem that only the first and third segments of the preceding state 
