CHAP, xv.] JOINTS OF ANTENNAE. 411 



one of its joints half-grown, is to suppose that in the comparatively 

 near past it was an instrument of totally different character from 

 that which it has in either of the two perfect forms. But no 

 such supposition is called for. With evidence that transitions 

 of this nature may be discontinuously effected the difficulty is 

 removed. 



The frequency of Meristic Variation in appendages is much 

 as it is in the case of body-segments. On the one hand there 

 are series containing high total numbers of repetitions little 

 differentiated from each other (e.g. the antenna? of the Lobster), 

 and in these Meristic Variation is common ; on the other hand 

 in series containing few segments much differentiated from each 

 other, such Variation, though not unknown, is rare. Of the 

 latter a few instances are here offered. That the} r are so few 

 may perhaps be in part attributed to the little heed that is paid 

 to observations of this class. Records of this kind might indeed 

 be hoped for in the works of those naturalists to whom the title 

 " systematic " has been given ; but unfortunately the attention 

 of these persons has from the nature of the case been drawn 

 rather to features whereby species may be kept apart than to 

 facts by which they might be brought together. 



From the lack therefore of records of such variations their 

 absence in Nature must not lightly be assumed. To quote but 

 one case : in the common Earwig the numbers and forms of the 

 antennary joints are exceedingly variable, but in many special 

 treatises on Orthoptera, I cannot find that this variability is 

 spoken of, and if alluded to at all the only notice is given in 

 the form "antennae 13- or 14-jointed." 



ANTENNAE OF INSECTS. 



PRIONID^E. 



I am indebted to Dr D. Sharp for the information that the 

 number of antennary joints in certain Prionidse varies. In Longi- 

 corns generally the number of joints is constantly 11. Dr G. 

 H. HORN of Philadelphia who is specially acquainted with this 

 group, has kindly written to me that of six species of N. 

 American Prioni four species have 12 antennary joints constantly 

 in both sexes. Besides these he gives the following cases of 

 Variation. It will be seen that in both of these the normal 

 number is much greater than it is in the other species 1 . 

 *616. Prionus imbricornis: females have very constantly 18 joints; 

 males have 18 to 20. A male in Dr Sharp's collection has only 

 17 joints in each antenna. 



1 In Prionus imbricornis and P. fissicornis doubt may be felt whether the trifid 

 apex should be reckoned as one joint or as two, but this applies equally to each 

 individual. I have counted it as one. 



