ATROPHY OF LIMBS BY DISUSE 



101 



Loss of limbs by disuse. Not only are one or both claws of a 

 single pair, or those of all the feet atrophied by disuse, but this pro- 

 cess of reduction may extend to the entire limb. 



In a few insects one of the claws of each foot is atrophied, as in the feet of 

 the Pediculidse, of many Mallophaga, all of the Coccidae, in Bittacus, Hybusa 

 (Orthoptera), several beetles of the family Pselaphidae, and a weevil (Brachy- 

 bamus). Hoplia, etc., bear but a single claw on the hind feet, while the allied 

 Gynmoloma has only a single claw on all the feet. Cybister has in general a 

 single immovable claw on the hind feet, but Cybister scutellaris has, according to 

 Sharp, on the same feet an outer small and movable claw. In the water bugs, 

 Belostoma, etc., the fore feet end in a single claw, while in others (Corisa) both 

 claws are wanting on the fore feet. Corisa also has no claws on the hind feet ; 

 Notonecta has two claws on the anterior four feet, but none on the hind pair. 

 In Diplonychus, however, there are two small claws present. (Kolbe.) 



Among the Scarabeeidse, the individuals of both sexes of the 

 fossorial genus Ateuchus (A. sacer) and eight other genera, among 

 them Deltochilum gibbosum of the United States, have no tarsi on 

 the anterior feet in either sex. si.- 



The American genera Phanseus 

 (Fig. Ill), Gromphas, and Streb- 

 lopus have no tarsal joints in the 

 male, but they are present in the 

 female, though much reduced in 

 size, and also wanting, Kolbe 

 states, in many species of Pha- 

 nseus. The peculiar genus Steno- 

 sternus not only lacks the anterior 

 feet, but also those of the second 

 and third pair of legs are each 

 reduced to a vestige in the shape 

 of a simple, spur-like, clawless 

 joint. The lingual joint is want- 

 ing in the weevil Anoplus, and 

 becomes small and not easily seen 

 in four other genera. 



krh -"= 



FIG. 110. Last tarsal joint of Melolontha 

 vulffarin, drawn as if transparent to show the 

 inner mechanism : un,, claws ; sir, extensor 

 plate ; , tendon of the flexor muscle ; vb, elas- 

 tic membrane between the extensor plate and 

 the sliding surface u ; krh, process of the un- 

 gual joint ; emp, extensor spine, and th, its 

 two tactile hairs. After Ockler, from Kolbe. 



Ryder states that the evidence that the absence of fore tarsi in Ateuchus is 

 due to the inheritance of their loss by mutilation is uncertain. Dr. Horn sug- 

 gests that cases like Ateuchus and Deltochilum, etc., "might be used as an 

 evidence of the persistence of a character gradually acquired through repeated 

 mutilation, that is, a loss of the tarsus by the digging which these insects per- 

 form." On the other hand, the numerous species of Phanscus do quite as much 

 digging, and the anterior tarsi of the male only are wanting. "It is true," he 

 adds, "that many females are seen which have lost their anterior tarsi by 

 digging ; have, in fact, worn them off ; but in recently developed specimens the 



