THE BIOGENETIC LAW 



181 



sixth and fifth to the fourth and third caterpillar stage, not in its 

 complete development, but in more and more incipient form ; and 

 nowadays the first traces of eyes, as we have already seen, are visible 

 in the course of the second stap-e. The markino- of the more remote 

 ancestors, the longitudinal striping, is now lost in proportion as the 

 eye-spots develop, perhaps because the former would take away from 

 tjie full efiect of the latter. The longitudinal stripes are still quite 

 plainly visible on the first three segments, but these segments are 

 drawn in and are scarcely noticeable when the caterpillar assumes 

 a defiant attitude (Fig. 4). 



In the case of marking with ring-spots, which is found especially 

 in species of the genus Deilei^Mla, the ontogeny discloses that it has 

 developed phyletically from the sub-dorsal stripe ; in the young stage 

 of this caterpillar also, the 

 sole marking is longitudinal 

 striping ; in Deilephila zy<jo- 

 phylli, from the steppes of 

 Southern Russia, this persists 

 apparently through all the 

 stages, but in the others it 

 disappears almost completely 

 in the later stages, but only 

 on the segments on which the 

 spot-marking has developed 

 from it. This happens in a 

 manner similar to that in which 

 the eye-spot in CliwrocaTnpa 

 arises, a piece of the white sub-dorsal stripe is enclosed above and below 

 by a semicircle of black, and later these semicircles unite, and cut 

 ofi" the portion of the sub-dorsal line, and form a black spot with a 

 light centre within which a red spot frequently appears (Fig. 117, J.). 



In most species these ring-spots occur on many segments (10-12) 

 (Fig. 117, i^), and in cases where they are of importance in making 

 the caterpillar conspicuous and easily seen they sometimes form 

 a double row. But we know one species, Deilephila }d2:)pophae8, in 

 which only a single ring-spot exists, and it is a large brick-red spot 

 on the second last segment, mimicking the red berry of the buckthorn 

 (Fig. 8, A and B, v). But individuals also occur in which there are, 

 on the five or six segments in front, smaller ring-spots which become 

 less distinct the further forward they are, and in most caterpillars it 

 is possible, on careful examination, to recognize little red dots on the 

 faded sub-dorsal stripes of these segments (Fig. 8, B). We might be 



Fig. 117. Caterpillar of the Bed-straw Hawk- 

 moth {Deilephila galii). A, Stage IV, sub-dorsal 

 stripe still distinct, the annular spots are still 

 incompletely enclosed in it. B, fully-formed 

 caterpillar without ti'ace of a sub-dorsal stripe, 

 but with ten annular spots. 



