of the Larva of Cnethocampa pinivora. 435 



Purpose of the Circulating Mass. 



It is possible that the circulating mass is sometimes formed 

 for the purpose of pupation, but again abandoned for the normal 

 procession on account of the unfavourable nature of the ground 

 in the spot selected. But this explanation cannot apply to the 

 majority of cases, for processions are of normal occurrence through- 

 out the insect's larval existence. 



Whether or not the circulating mass be a "rest formation" 

 (as has been suggested) it is not impossible that it may possess 

 other advantages as well. The facts already mentioned suggest 

 the possibility of there being a regular arrangement within the 

 circulating mass itself In this case the formation might be a 

 means of altering the order of the larvae whilst retaining the 

 same leader. Other facts may be mentioned pointing to the 

 same conclusion. Processions arranged artificially, by removing 

 larvae at random from a mass and placing them in a position 

 of head-to-tail contact, were not found to retain their original 

 order for very long. A circulating mass was always formed and 

 a different order arranged for the subsequent procession. The 

 formation of a mass, in this case, however, was due probably to 

 external interference rather than to any fixed habit of altering the 

 order of the procession. 



Method of Pupation. 



Larvae which had become isolated, from any cause, were 

 observed to bury themselves in the soft sand by means of their 

 mandibles; but as a general rule processions seemed to burrow 

 collectively in the following way. A circulating mass was first 

 formed in a position which the primite apparently selected, after 

 testing the consistency of the sand with his mandibles. On two 

 occasions, which came under my observation, the process differed 

 slightly, in that the original procession voluntarily broke up into 

 several smaller processions of twenty or so each — in a manner 

 similar to that described by Fabre — each of which formed a 

 circulating mass and buried itself independently. As soon as the 

 circulating mass was formed the whole commenced to rotate, thus 

 producing a depression in the sand which gradually deepened. 

 The sand was at the same time loosened, and some was thrown up 

 on to the top of the mass. All the while the larvae were deposit- 

 ing their silk threads until a regular network was formed round 

 the mass, in which sand became entangled. In some cases the 

 lower larvae appeared to assist in the process by attacking the 

 sand beneath with their mandibles. As the process continued 



