74 ILLIXOIS BIOLOGICAL MONOGRAPHS [316 



Strongly indicates that the spinneret functioned unequally in different 

 instars in the primitive caterpillar of the family. The spinning of silk most 

 probably occurred in the last instar or in both first and last, these two con- 

 ditions being the only ones of general occurrence in forms which retain the 

 primitive long spinneret in the fully grown larva. Thus the factor of 

 unequal function in the postembryology of the spinneret of noctuid larvae 

 is most probably an ancestral one. In Type IV this factor has become 

 secondarily eliminated by the loss of the power to spin silk in both first and 

 last instars. We cannot reasonably expect, therefore, that recapitulation 

 would find expression in the postembryology of this type with respect to 

 the relative length of the spinneret. 



As previously concluded in the treatment of the morphology of the 

 spinneret the fringe is a specialization which has developed in correlation 

 with the habit of subterranean pupation, apparently functioning as a brush 

 for the Hning of the earthen cell with a secretion of the silk-glands. The 

 fact that it is well developed only in the last instar also supports this con- 

 clusion. The four types of the development of the spinneret just discussed 

 are based only on its relative length and do not apply to the fringe, which 

 often appears in both Types II and IV where the reduced spinneret occurs 

 in the last instar. The appearance of the fringe in postembryonic develop- 

 ment apparently represents a recapitulation. Since it functions only in the 

 last instar, however, the factor of unequal functions has operated in the 

 same direction as the recapitulative force, so that this process is not the 

 expression of recapitulation alone. It falls under the same group in our 

 classification of postembryonic changes as the development of the adfrontal 

 suture, recapitulative and adaptive to unequal function. 



The appearance of the lateral emarginations, which are present only in 

 the reduced type of spinneret, have presumably developed in phylogeny as 

 they do in postembryology. Since the upper and lower lips thus formed 

 probably have to do with the function of the spinneret, which is performed 

 only in the last instar, unequal function as well as recapitulation has oper- 

 ated in the production of this postembryonic change. 



The appearance of the elongated proximal fold and of the secondary 

 chitinization in the postembryonic development of Folia renigera (Figs. 29, 

 32) also recapitulates the phylogeny. Since these structures serve as a 

 support for the spinneret, which is functional only in the last instar, unequal 

 function also plays its part in these changes, which are evidently to be 

 regarded as recapitulative and adaptive to unequal function. 



The reduction in the relative width of the proximal sclerite is apparently 

 of general occurrence within the family, this process always manifesting 

 itself regardless of the trends of development along other lines. Until more 

 definite knowledge is gained of the phylogeny of this sclerite no definite 

 conclusion can be reached as to the significance of its reduction in relative 



