14 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



In Eacles imperial ifi, stage I (PI. XLVII, fig. 2, ii), the niidtubercle is large, highly devel- 

 oped, each //' being subdivided or two-headed. In stage III it lieconies smaller in proportion, 

 a little longer than the diameter of the caudal horn at its base, and four-headed; it becomes 

 shorter in stage IV and after the last molt is still more reduced and is forked, but no higher 

 than broad. 



In Citheronia 7-egidis{F\. LI V) this spine is, in accordance with the rest of the armature, 

 much more developed than in the other genera. It is in stages I, II, III about half the thickness 

 and length of the caudal horn, repeating its shape and spinulation, while in stages IV and V it is 

 about a third as long. 



In C. sjjIendenK, in stages IV and last, it is about two-thirds as long as the caudal horn, 

 while in the last stage of C. sejndcralis it is much shorter, onl}- about one-fourth as long as the 

 caudal horn. 



The thoracic arniature. — We will ))egin with Adelocephala, whose matui'e larva is through- 

 out the body the most spiny, the abdominal segments between the tirst and the eigiith bearing 

 the caudal horn, being armed with large, and in certain species conspicuously colored, spines or 

 horns. The group is remarkable for the enormous thoracic and caudal horns in the earliest 

 stages. 



In stage I of A. licolor (Pis. XLV and XLVI) and of Si/ssphinx vioUna (PI. XLVII), the 

 remarkable features are the enormously developed second and third thoracic tubercles or horns, 

 which are three times as long as the caudal horn. While the specific and generic differences are 

 given in detail under the special description of each life history, we may here give a comparative 

 account of the form and history of the thoracic spines in the Ceratocampina?. 



The prothoracic segment in the two genera already named is usuall}- provided with setiferous 

 tubercles of even less than normal size, the dorsal ones no larger than the lateral ones, there being 

 six on each side of the segment. But in the undetermined mature Brazilian larva (PI. Ill, fig-. 1, 

 and PI. XLIX, tig. 4), they may be found in stage I when discovered to be long and well 

 developed; they are distinct, fairlj' long pi-othoracic dorsal spines. 



In Eacles and Citheronia, however, there is a great change; those of the dorsal pair being 

 enormously developed, and ending in a fork or two twin setiferous tubercles, repeating the 

 two forms of those on the two hinder thoracic segments. In Eacles the dorsal spines or horns are 

 between one-fourth and one-third as long as those behind, have two to three secondary tubercles, 

 and end in two long diverging setiferous branches or tubercles about a third as long as the entire 

 horn. This 'form is repeated in the subdorsal horn, which is of the same general shape, but with 

 a shorter main shaft. 



Of the horns behind, those of the mesothoracic segment are a little longer than the mcta- 

 thoracic ones. In Eacles the tubercles of the supraspiracular series are alike on each three 

 segments in being primarily two-headed, but with such large secondary' setiferous tubercles as 

 to make them appear tive-headed. The infraspiracular spine on the first thoracic segment is 

 veiy large, three-headed, while the one below is double headed. There are in all five tubercles 

 on each side of this segment. It is to be observed that in Eacles and Citheronia there is, con- 

 trary to Adelocephala and Sj'ssphinx, a close similarity in shape and size between the caudal horn 

 and the thoracic hoi'ns. 



In Oitheroiiia regally, the dorsal prothoracic horns arc still more similar to those behind, 

 being nearly as long, and of identical shape and similarly spinulated. There is a marked differ- 

 ence in the development of the subdorsal horns of Citheronia, these being very much longer than 

 in Eacles, and only slightly differing in the shape of the bulbous end. The greater specialization 

 of the swollen end of all the eight horns as well as of the caudal horn in Citheronia is of 

 interest. The bulb is shaped like a chestmit, full, thick, forming the couuuon base of the two 

 diverging tubercles, which bear specialized set;« in the form of cylindrical straight rods, blunt 

 at the end; a seta of very characteristic shape. This style of specialized seta also occurs in the 

 thoracic horns of Adelocephala and Syssphinx, though in the caudal horn it docs not appear, the 

 setaj being of their primitive shape. 



