EEPOET OF THE ENTOMOLOGIST. 235 



by tlie observations of M. C Hill, of northeastern Ohio, who likoAvisc 

 found that the small form is very much less numerous than the larj^-y one. 



-' The truest test of the specific distinction of these two forms lic\s iu 

 the comparative shape of the male genitalia, and the accompaiiyinjx 

 fi;;ures (c, ^, e, and/, in Fig. 1, PI. VI), from drawings made in ]S(»8 by 

 I)r. II. A. Hagen, of Cambridge, Mass., show the male genital hooks of 

 both. That of septendecivi is represented on the outside at e, on tlio in 

 side at d ; and that of cassinii on the outside at e, and on the inside ;it /'. 



" B}' these figures it will be seen that there are sufficient differences 

 to separate tbe two forms as distinct ; but while the hooks of the l;iri;<' 

 kind [scpiendecim) are quite constant in their appearances, those of tlic 

 smaller kind {cassinii) are variable, and in some few specimens an' in- 

 distinguishable from those of the large kind. The circumstance, coupled 

 with the fact that the small kind regularly occurs witii botii the 17 and 

 13 year broods, would indicate it to be a dimorphic form of the larger, 

 and only entitled to varietal rank. 



"The large form has been observed to make its appearance from eight; 

 to ten days earlier than the small form {cassinii), and there is not a 

 single specimen of the latter among a number of the 13-year brood 

 {tredecim) that I captured in IMay, 1868, tliough I took a few specimens 

 afterward." 



The scptendecim and ircdccim forms have been looked upon by some 

 writers as constituting distinct species, notwithstanding their external 

 resemblance. There are absolutely no differences observable in the in- 

 sects constituting the different broods other than the difference of time 

 required for underground development. 



Tbe species should be catalogued thus: 

 Cicada septendccim Linn. 



Eace tredecim Kiley. 



Dimorphic variety cassinii Fisher. 



Our correspondence shows that there is an astonishing confusion as 

 to the relation of the two varieties with the periodic or sepicndecim and 

 tredecim races. Many observers, and even well-known entomologists, 

 have taken the varieties to represent the races; audit cannot be too 

 strongly urged, because of the important bearing of the facts on cor- 

 rect chronological information, that while the variety cassinii can al- 

 ways be distinguished from the typical form, tlie two races include both 

 varieties, and are absolutely indistinguishable, except for the different 

 jn'rioils of larval existence. 



THE LONG PERIOB OF UNDTlHaEOUND DEVELOPIilENT. 



The quoted passages which follow are from a paper read by us at the 

 mt'oiiiig of the Biological Society of Washington for May 30, 1885, and 

 subsequently published in \)?ixt\n.i\iQ. Scientific American (June 27, 1885, 

 yupjil.) and Science (June 25, 1885, vol. v, p. 518-521). 



" From chronological data the fact that seventeen years or thirteen 

 \ ears are respectively required for the underground development of this 

 insect, according to the race, is fully established, one of the first recorded 

 septendechn broods having beeu observed every seventeen years since 

 1715. Sitch anomalous and exceptional facts in natural history, as wit- 

 ness the discussion as to the egg-laying of the Ornitliorliynclius, always 

 provoke skepticism, and the facts recorded regarding our Cicada's hypo- 

 gean life have shared in this tendency. Hence a few biologic facts, 

 especially such as bear on the development of the larva, will not prove 

 uninteresting. 



