FROM THE CARBONIFEROUS FORMATION. 145 



dorsal plate is not perforated for foramina repugnatoria, 1 but as means of defence it is 

 armed with huge spines upon either side ; one row (for they occur on all the segments) lies 

 above, near the middle line of the body ; another lies low down upon the sides near the 

 lower margin of the dorsal plate ; and a third row is sometimes interposed between them. 2 

 These spines are similar in all the rows, but differ in the different species ; in few prob- 

 ably are they simple but provided with spinules to a greater or less extent. In the most 

 bristling the spines are forked at the tip, and besides this have a basal corona of stout 

 spinules ;, others have such a whorl of spinules in the middle of the spine ; in nearly all the 

 spines are at least half as long as the width of the body, and sometimes they are nearly 

 as long. These spines are in themselves very remarkable and resemble nothing that I 

 can discover in modern Arthropoda, 3 unless it be certain thorny spines seen in the early 

 stages of some Crustacea, and especially of some found on the tail piece of cirrhiped lar- 

 vae, figured by Claus, to which Mr. Alexander Agassiz has called my attention. Some of 

 his own unpublished drawings of the young of our common barnacle exhibit still closer 

 resemblances, although even here it is not very marked. These spines are fixed, and one 

 can readily picture the difference in external aspect between one of these creatures a foot 

 or more in length, bristling all over with a coarse tangle of spines, and the smooth coiling 

 lulus of the present day. (See PI. 10.) 



If we pass, however, to the ventral plates we shall find differences of even greater sig- 

 nificance. In the modern Diplopoda, as already remarked, these plates are minute ; they 

 are similar in size and form ; the anterior one forms the anterior edge of the segment, con- 

 tinuous with that of the dorsal plate ; together, however, they are not so long as the dorsal 

 plate at their side, and the latter appears partly to encircle the posterior plate by reaching 

 inward towards the coxae of the legs ; the legs are attached at the posterior edge, and 

 those of the opposite sides are so closely crowded together that they often absolutely touch 

 each other (Fig. 1) ; the stigmata, of which there is a pair to each ventral plate, are placed at 

 the outer edge rather toward the front margin ; they are minute, and have their openings lon- 

 gitudinal as regards the animal, i. e., they lie athwart the segment ; the coxae of the legs of 

 the anterior plate are therefore opposite the stigmata of the posterior plate. No other 

 organs are found upon the ventral plates ; one might indeed say there was not room for 

 them. The legs themselves are composed of six cylindrical simple joints, subequal in 

 length, the apical armed with a single terminal claw ; the whole leg is short, rarely more 

 than half as long as the diameter of the body. 



In the ancient types all is very different. In the first place the ventral plates, which 

 are of equal size, occupy the entire ventral surface, and perhaps may be said to extend 

 partly up the sides of the rounded body, and no part of the dorsal plate passes behind the 



1 This is what would be expected from the presence of forked spines, microscopic indeed, fringing the last abdomi- 



spines; two such means of defence should not be looked nal segment of the female, and occurring, he says, only in 



for in the same animal; offensive glands are present only the sub-family Diaspinae. 



in slow-moving, or otherwise defenceless creatures, as in The spines of these myriapods have nothing to do with 



Phasmidae among Orthoptera for example. the barbed hairs on the body of the embryonic Strongylo- 



8 In one species there is only one row of spines on either soma as figured by Metschnikoff (Zeitsch. f. wiss. Zool., xxiv, 



side, situated where the third row occurs in the trebly spined pi. 26, fig. 1 «.). These latter are comparable with the der- 



forms. mal appendages of the embryonic larvae of Lepidoptera 



8 Since this was written, Mr. J. II. Comstock has shown See my Butterflies, pp. 28-32, figs. 36, 37. 

 me his capital drawings of Coccidae and pointed out to me 



MEMOIRS BOST. SOC. NAT. HIST. VOL. III. 19 



