464 



time, but this is probably to be looked upon as an 

 abnormality. 



The vesiculae seminales have meanwhile been enlarging, 

 and now project forwards as a pair of great thick-walled out- 

 growths from the lower portions of the two vasa deferentia. 

 The wasp is, then, provided with three vesiculae seminales, 

 two-paired, and mesodermal in origin, formed as dilatations 

 from the lower portion of the two vasa deferentia, the other 

 a single forward dilatation of the cavity of the penis, as 

 described more fully above (fig. 27). The cavity of the penis 

 is developed about this time, and, shortly after, the lower 

 parts of the vasa deferentia open into it. 



At this time, too, the testes are beginning to elongate 

 and extend forwards. The spermotogonia still measure 5/x to 

 6/x in diameter. 



During the next twenty-four hours the male organs grow 

 rapidly. The vesiculae seminales elongate somewhat and 

 become ''sausage-shaped." That portion of the vas deferens 

 which has opened into the penis now increases in length ajid 

 pushes the paired vesiculae upwards, so that they now come 

 to lie more towards the middle of the abdomen. The testes, 

 themselves, meanwhile have elongated still further, and are 

 now situated dorsal to the intestine, just below the body wall. 

 Their own growth, and the elongation of the vasa deferentia, 

 result in their now occupying the upper regions of the fifth 

 and sixth abdominal segments, having migrated through the 

 seventh and eighth segments during larval and early pupal 

 life. 



In the two-day pupa the opening-s of the vasa deferentia 

 into the penis have become very wide; except for this change 

 no marked alterations are visible in the male organs. The 

 spermatogonia are still 5jut to 6/x in diameter. 



In the three-day pupa the testes fuse anteriorly above 

 the intestine, and with this change, attain their mature 

 proportions. 



Tliroughout the whole of larval, and the greater part of 

 pupal life, the spermatogonia remain at a fairly constant size, 

 viz., 5/1 to 6/x. Sperm formation begins in the three-day 

 pupa; I have, however, seen cases where precocious sperm 

 formation took place in the pupa of thirty-six hours. Tlie 

 sperm has a rounded head about 2/x in diameter; the mid- 

 piece is generally quite distinct and the tail very long (about 

 28;.). 



The frequent precocious development of the spermatozoa 

 is especially curious; thus, while pupae three days old may 

 be quite devoid of tailed spermatozoa, the pupa of fifty-six, 

 and even thirty-six hours, may have testes which are abso- 

 lutely crowded with sperms. 



