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MILLIPEDS OF FAMILY LYSIOPETALIDAE — LOOMIS 103 



On account of the repetition of the same features in so many seg- 

 ments, the millipeds afford unusual opportunities for observing the 

 precision of adjustment of the characters, as in the study of heredity 

 in twins or in pure lines, which are supposed not to vary. With 

 many segments the same, even slight changes of the characters are 

 noticeable and significant, as are small deviations when using an in- 

 strmnent that carries a vernier. 



SPECIALIZED CHARACTERS OF THE LEGS 



The anterior legs of both sexes of Lysiopetalidae, in all the species 

 examined, have a comblike row of bristles along the inferior face of 

 the terminal joint. These combs are regularly present on the first and 

 second pairs of legs, and in some cases they are found on the third 

 pair. Extension of the combs to the third pair of legs has been noted 

 in the females of S'plrostrephmi and in males of Colactis and Heftiuni. 



The males of most of the species have the terminal joints of some 

 legs provided with fleshy, pubescent pads on the under side. The 

 number of legs so provided is not the same in the different species, and 

 a few species lack this feature. The pads are absent in two species 

 of Colactis and in the genus Heptium. 



In all cases where the pads are found they begin on the legs imme- 

 diately following those provided with combs, and all the remaining 

 legs in front of the gonopods have pads, and at least a few of those 

 behind the gonopods. In one species, Diactis soleata^ the pads extend 

 far back, within 10 or 12 legs of the end of the body. In a related 

 species, D. triangula, the pads do not reach the middle segments. 



Males of the genus Diactis have a process on the basal joint of the 

 anterior pair of legs of many segments near the middle of the body, a 

 feature not present in the other genera. 



The seventh pair of legs of the male is specially reduced and modi- 

 fied in the genus Heptium, leaving only six pairs of normal legs in 

 front of the gonopods. The basal joint of the seventh leg is produced 

 into a long erect spine, standing in front of the gonopod and nearly 

 its equal in length. The outer joints of the modified leg are very 

 small, especially beyond the third joint, but the number of joints ap- 

 parently is the same as in the normal legs. In one individual of 

 Heptium a marked difference between the legs of the seventh pair 

 was observed, one of the legs being but slightly reduced and having 

 the spine of the basal joint replaced by a setiferous papilla. It may 

 be inferred from this variation that the specialization of the seventh 

 legs is relatively recent. Also it is possible to consider the develop- 

 ment of a spine on these legs as a carry-over from the gonopods. 



