MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 39 



3. The double piliferous tubercle 07i the ninth nromere becoming obsolete in Stages IV and V. 



4. The abdominal region is longitudinally striped with dark and whitish bands, but there are 

 no transverse marks in Stage I or iu later stages. 



B. EVOLUTIciN OV LATER AD.VPTATIOXAL CHARACTERS. 



1. The head slightly angular, face subtriangular, with a light-brown or greenish lateral stripe 

 (Stages II-V). 



2. Appearance of a transverse row of dorsal graiuilations on the hinder end of each segment 

 in Stage II, persisting through larval life. 



3. The eight thoracic spines lose their bulbous tips and become simply slightly forked in Stage 

 III and later. 



4. The two dorsal spines of uromeres 1-7 are in Stage II larger than the others; in Stage III 

 they become ivory white externally and in Stage IV larger and silvery white on the outside. 



5. In the last two stages the eight thoracic spines become very much shorter in proportion to 

 the size of the body and become less movable; as they decline in size and functional importance, 

 the metallic, silvery, dorsal spines on the abdominal segments become conspicuous and apparently 

 useful to the larva. 



The following sumin;uy of a better-known caterpillar, that of EticJes imjicrialis, will bring out 

 more clearly, perhaps, the point we wish to make, i. e., that the later adaptational characters have 

 been acquired during the lifetime of either one or of a series of ancestral forms leading ui) to the 

 present one. 



SUMMARY OF THE CHIEF ONTOGENETIC FEATURES OF EAGLES IMPERIALIS. 



A. CONGENITAL CHARACTERS. 



1. In Stage I there are three pairs of very long dorsal deeply forked thoracic horns, nearly 

 half as long as the body, 



2. A similar median spine on tlieeighth abdominal segment, with one half as long on the ninth. 



3. The abdominal segments are transversely banded with black. 



4. The lateral spines on the abdominal segments bitid and nearly as large as the subsimple 

 ■dorsal ones. 



5. Body pale chestnut brown ; head light reddish. 



6. The spiracles minute and difficult to detect, as they are situated iu one of the transverse 

 ■black bands. 



B. EVOLUTION OF LATER ADAPTATIONAL CHARACTERS. 



1. The forks of the larger dorsal spines disappear at the end of Stage III. 



2. The dorsal thoracic spines become recurved in Stage III. 



3. The dorsal thoracic and caudal horn become much shorter and stouter in Stage IV, when 

 the characters of Stage V (and last) are nearly assumed. 



4. In Stage II the dorsal spines on the prothoracic segment begin to grow shorter and stouter. 



5. In Stage II the large horns begin to be less deeply forked. 



6. The transverse black stripes disappear at the end of Stage II. 



7. The dorsal and lateral spines on abdominal segments 1-7 are nmch smaller in proportion 

 in Stage III than in Stage II. 



8. Toward the end of Stage III the colors of the body become more conspicuous and variable. 



9. In Stage III the spiracles become parti-colored and very conspicuous. 



10. The dorsal thoracic and the ''caudal horn "become much shorter in Stage IV and not 

 forked at the tip. 



11. The hairs become long and abundant in Stage IV. 



12. The body in Stage IV becomes much stouter and heavier than before, while the head has 

 not greatly gained in size proportionately. 



The European Aglia tau appears to be the sole representative in the Old World of the' 

 American group or family Ceratocampidie, though with the larval, pupal, and imaginal characters 



