March, 1912.] Newcomer: Relations of Ants and Caterpillars. 33 



I have, on various occasions, seen an ant touch the organs before 

 they were entirely evaginated. They were at once withdrawn, the 

 ant showing no signs of excitement. If it is a tactual irritation which 

 distracts the ant, this failure to become excited on the part of the 

 ant, when it touches the partially protruded organs, would be ex- 

 plained by the fact that the setae occur only on and near the tip of the 

 diverticulum, and would not yet be exposed. While watching the 

 ants, I noticed that occasionally one of them touched the fully ex- 

 tended organs with its antennae, without appearing to be affected 

 thereby. One ant in particular was not thus stimulated during one of 

 my observations. A half hour later, the same ant ran about wildly 

 whenever its antennae came in contact with the extended organs. I 

 cannot explain this occasional insensibility of the ants. 



The action of the organs of the larva seems to be a reflex caused 

 by the stimulus of the ant's stroking the surface of the body. When 

 this stimulus, which is evidently transmitted by the tactile hairs, is 

 present, one of two things occurs. If the sac in the tenth segment is 

 in a condition to exude a drop of liquid, it is everted, and the liquid 

 is forced to the exterior. When this condition does not obtain, the 

 organs on the eleventh segment are thrust out. The evagination of 

 one or both of the organs, when there is no ant present, must be 

 caused bv the relaxing of the retractor muscle due to some other 

 cause. I had one larva which had one of these organs continually 

 thrust out, and rough handling or contact with an ant did nat cause 

 it to be withdrawn. Apparently the retractor muscle had lost its 

 power of contraction. 



I can offer nothing new in regard to the protection afforded the 

 larvae by the ants, except what I have already given (3) in respect to 

 the larvae of L. fnlla. Here, the commonest parasite that I found was 

 a Tachinid. I found the eggs of this on many larvK in the first and 

 second instars. The ants were not attracted to the larvae until the 

 latter had reached the third instar. I did rear a Braconid from one 

 larva, and it is probable that there are other parasites. I have 

 observed no parasites in rearing L. piasus. The external opening of 

 the glands in these species is present in the second instar and the 

 evaginable organs appear in the third instar. 



The slit already mentioned occurs on the caudo-dorsal part of the 

 tenth body segment (Fig. i). It is about 0.5 mm. in length and 



