THE CATERPILLAR: INTERNAL ORGANS. 35 



in length and become the efferent ducts ; where they enter the sac there is 

 at the first a shght bulbous enlargement, and it is just here that the most 

 remarkable growth takes place ; the bulbs increase so as to become notice- 

 able ; then a constriction takes place in their connnon union with the sac ; 

 the neck prolongs to what is finally a slender tube, the ductus ejaculatorius, 

 as large as one of the efferent vessels and much longer than the whole body 

 of the insect, leading into the intermittent organ of the male ; while the 

 bulbs grow in a similar way to form a pair of tubular glands or seminal 

 vescicles, into which, shortly before their union to form the duct, the efferent 

 vessels open ; and these various slender organs, — vessels, glands and duct 

 are at maturity enwrapped and intertwined in a most intricate, common 

 and indistinguishable, but loose, convoluted mass which fills the last four 

 seefments of the abdomen. 



The testis is clas[)cd by fine tracheal vessels which suddenly expand 

 from the larger tube of one of the main stems arising in the fifth abdominal 

 segment. In the mature chrysalis it is crammed with sijermatozoa, which 

 in Aglais are of two sorts, one larger though only about three-quarters of a 

 millimeter long and pretty regularly tapering, the other shaped as clubl)ed 

 filaments less than a quarter as long. 



The changes in the female organs are exceedingly similar. With the 

 shortening of the body, the first change is in the sinuosity of the thread 

 which unites the ever separate ovaries to the pair of sacs beneath the anal 

 orifice ; concomitantly the base of the four terminal threads of the ova- 

 rian mass begin to separate from each other, and this portion of the ovarian 

 tubes practically remains merely a set of ducts, the parts beyond forming 

 the ovary proper, developing enormously and containing eggs, usually in 

 varying stages of development in each of the four tapering tubes of 

 which it is composed on each side of the body, and which are united 

 again at the tip, and are then fastened to the wall of the fourth ab- 

 dominal segment above. But the important new developments arise, as in 

 the male, just at the hinder extremity of the oviducts, for in a similar way 

 wholly new organs are rapidly developed. The single accessory gland 

 and the copulatory pouch originate on opposite sides, in an entirely similar 

 manner to the paired accessory gland. All are at first mere bulbous ex- 

 crescences of the base of the thread mentioned. But some develop from this 

 beginning in one way, some in another, until in the mature pupa all the 

 appendages of the butterfly are fully developed. 



Development of the Tvings. Inasmuch as most of the changes in the 

 organs from the larval condition to their perfect development take place in 

 the intermediate quiescent state, we may here say a word about the de^ el- 

 opment of the wings, which first apjiear as external organs in the pujia, 

 although they should more properly have been considered in the preced- 

 ing section, since they arise and develop in the larval period. In the 



