18 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



Ill Citheroitia nyalls, sluf^e 1 (PI. Ll\'), tlie relations are luueh as in Eacles. Tlie caudal spine 

 is a nearlv exact repetition of the twelve thoracic ones, ending- in a similar Inilbous body formed 

 by the fusion at their bases of the two terminal tubercles, each division or fork ending in a thick 

 blunt rod. 



In stage II the cauilal horn again repeats tlie now somewliat moditied shape of the horns on 

 the thoracic segments (tig. 1), ending in two miequal spines. 



In stage 111 the caudal horn is of the same proportionate shape and height (tig. 3). 

 In the last .stage the caudal horn is high and j)rominent, being as large as the sulidorsal 

 thoracic horn, spinose, and distinctly forked at the end (tig. <i). 



In C. xj>le)idt'iis (PI. LV, tig. hi, Ih /') the horn is nuieii sliorter. but still bitid at the end: 

 in f. srj))il('riili!< (tig. 4'/, 4i) it is much longer, l)ut still ends in two minute tubercles; in < '. hini-iKin 

 (tig. -1, h) it is rather shorter and slenderer than in the other species mentioned. 



Anisota ditiers remarkably from the other genera of its group in having no caudal horn on 

 the eighth abdojninal segment, the primary setiferous tubercles / not being crowded and fused 

 into one after the first molt, the cliaracteristics of stage I being retained throughout larval life, 

 tlie four primary dorsal setiferous tubercles being arranged in a trapezoid. It should be noticed 

 that the eighth abdominal segment is not any narrower than the seventh, while the ninth is nuich 

 narrower, the body ratlier suddenly narrowing to the end of the suraual plate. A\'hether this 

 width of the eighth segment has caused crowding and the fusion of the tubercles / is a matter 

 worth considering, though in Adelocephala and C. rrtjidia the eighth segment appears to be as 

 wide as the seventh. Yet it remains a fact that in Aiusota there is no fusion of tubercles /, no 

 median dorsal horn, whereas there is a fusion on the succeeding segment and a resulting median 

 tubercle. Its history is given on page 13 and the reader is referred to Pis. L-LIII, which 

 illustrate the development of this ninth uromeral caudal or median horn in Anisota. 



Here the question arises whether the lack of fusion of tubercles / on the eighth uromere is 

 due to inheritance from some notodontian ancestor, to reversion, or is simply the result of 

 disuse, resulting iii reduction and partial atrophy. When we take into account the close 

 relationship between the moths of Anisota and Adelocephala, the incongruity ))etween the larval 

 .stages in respect to the armature of the end of the body seems remarkable. 



It is to be observed that the ninth uromeral tubercle or median horn in the final stage shows 

 its doul)le origin in being bitid at the end like that on the caudal horn of the eighth segment in 

 other genera than Anisota. 



This ninth uromeral tid)(>rcle is well developed in all stages in Eacles and Citheronia 

 PI. LIV (tig. <!)' but exists in a niu<-h reduced comiition in Adelocriiluila and Sysspiiinx of the 

 first to the final stage. 



The ciKiihd linni hi tin- jS'otddontidiv.—lw only two groups or families is the caudal horn a 

 nearly persistent characteristic common to nearly every genus of these extensive groups— I 

 refer to the Ceratocampida' and Sphingidiv— while the more specialized Hemileucidic and Satur- 

 niida' have a similar double median tubercle, which retains its rounded or clavate form. Else- 

 where the fusion of the tubercles / on the eighth uromere is a sport, alierration, or. better, a 

 mutation, which has become fixed by heredity. Such is the caudal horn of Boinhtj.r inari, of 

 Fndroiiu's vcrs/rn/ni;/. tlie earliei' stages of Brahmaeida>. and of certain Notodontida\ 



Its appearance in tiiis group we will first discuss, since their stages of evolution have been 

 examined and ilUistrated in my monograph of this family. In this group the larva' before the 

 first molt iia\c the primitive arrangement of the four dorsal setiferous tubercles (/, //) arranged 

 in a trapezoid, as seen in the freshly hatched larva of Lophodonta. Pheosia. Dasylophia, 

 Ilvparpax, Schizura, and Ilcterocanipa. A caudal horn or tu))ercle arises in the ontogeny of 

 the larva in four genera, i. c., Pheosia. Dasylophia, Hyparpax. and Schizura. 



Tlie tubercle is most characteristic in Pheosia. being like that of Sphinges, Bomhy:vmori, and 

 ceratocampids. except that it is smooth and not solid and tul)erculated. If the reader will turn 

 to PI. XX of my monogi-aph of the Notodontida> and consult the description of the early stages 

 he will obtain an idea of the mode of origin of the so-called horn. In stage I the arrangement 

 of the dorsal and subdorsal setiferous tubercles is plainly drawn. The pair of tubercles / on the 

 eighth abdominal segment ai'e. at the birth of the lar\a, crowded together, their bases forming a 



