1907.] Wheeler, The Polymorphism of Ants. 7 



only pupae at the very critical moment when they have just been stripped of 

 their larval skin by the workers and are, therefore, little more than semipupse, 

 for obviously at this moment the cuticle is thinner and will be more easily 

 pierced by the young Orasema larva than during the preceding or succeeding 

 stages. And in the fourth place, she does not lay her eggs at random any- 

 where on the body of the semipupa but carefully selects one of four regions 

 near the head. Usually she places the egg on the sternal surface just 

 beneath the still very short, incurving legs of the semipupa but occasionally 

 it is placed on the back of the neck between the head and the prothoracic 

 segment, or on the right or left side of the neck beneath the corresponding 

 prothoracic leg. These regions would seem to be singularly appropriate, 

 both because the cuticle of the semipupa is extremely thin and readily 

 punctured by the parasitic larva at these points, and also because the egg or 

 resulting larva, especially when it is covered with the overlapping appendages 

 of the semipupa, is not so readily brushed or licked off by the instahilis 

 workers. I believe that the danger of detaching the egg is very great and 

 this, together with the other special requirements above enumerated, may 

 account for the fact that comparatively few of the great number of Orasema 

 €ggs ever complete their development. 



Further reflection shows still greater appropriateness in the time and 

 place selected for oviposition by the mother Orasema. In the sexual semi- 

 pupse of instahilis, and especially in those of the soldiers, the small an- 

 terior end of the body is destined to grow very rapidly and to undergo 

 -extraordinary changes in structure. For this purpose carefully elaborated 

 liquid substances of a very high nutritive value are suddenly propelled into 

 the anterior portion of the body of the semipupa, which therefore appears 

 tense, clear, and transparent in this region, while the abdominal region is 

 full of opaque, nonmetabolized fat cells. The parasitic larva is thus sit- 

 uated from the first at a point where it has ready access to a rich food 

 supply and is able to grow with surprising rapidity. 



The instinct that leads the mother Orasema to oviposit with such pre- 

 cision is not, however, infallible. As the number of soldier and sexual 

 pupse in an instahilis colony is always very limited compared with the num- 

 ber of worker pupse, the Orasema, impelled, apparently, by the need of get- 

 ting rid of her eggs, sometimes oviposits on the latter, although even in such 

 cases also, she chooses the cervical and sternal region. The interesting 

 ■consequences of this instinct aberration will be considered in a later para- 

 graph. 



Several of the youngest Orasema larvje seen are represented in Plate II, 

 Figs. 30-35. They are extremely small — less than .1 mm. in length — 

 and of a dark brown color. The head is distinct and furnished with short. 



