on [January, 



4. In another 10 or 15 minutes every larva has extricated all but the last 



abdominal segment. 10.45 a.m, 

 6. Immediately they began to spin up. By 11 a.m. each larva had spun 



a loose outer net halfSvay up its body (text-fig. 4, w). 



6. In the following hour only the tip of the head jn-otruded (text-fig. 2, on 



right side of jm). 12 p.m. 



7. By 3 P.M. the outer network of the web was finished and the inner 



closely woven shell was in process of formation, though the larvae 

 could still be seen through, working steadily. 

 Complete time from beginning of emergence, 5^ hours. By the following 

 morning the cocoons were nearly completed as far as one could judge 

 from an external examination. 



A striking fact is the apparent synchronism in the inception of the 

 outward movement by every larva. Some stimulus evidently becomes 

 passed from one to the other. Kept on one's desk and occasionally 

 examined, a box of " sleepy " Pierine caterpillars are at one moment 

 normal. In the space of ten minutes or so, an individual may i-esolve 

 into a mass of struggling white maggots, as drawn in text-fig. 1. The 

 change is renrarkable, and the question naturally arises as to what is the 

 nature of the stimulus which sends every larva rapidly boring outwards. 

 1 believe that the outward movement is not really so synchronous as 

 cursory examination seems to show ; what probably occurs seems to be 

 that when the larvae are full-grown, their imaginal discs, silk glands, 

 and general histolytic processes having arrived at the correct stage, an 

 inward physiological stimulus arises in a few of the most advanced indi- 

 viduals, and it is their struggles outward that sets the others working 

 likewise. 



In this connection some interesting facts have been noticed. In 

 .such a case as that shown in text-fig. 1, almost every individual has 

 attempted to work outwards in the middle third of the body ; this 

 region is crowded, but not all larvae have succeeded in their fight for a 

 space in this favourite region ; ten minutes after the stage shown in text- 

 fig. 1 more larvae began to appear in the thoracic and the hind abdominal 

 regions. These larvae were not immature in size, and I considered that 

 their lateness in appearance was due to the fact that they had been 

 unable to obtain a footing in the mid-region, and liad been forced to 

 work along underneath their more successful fellows to gain a place for 

 commencing boring operations. 



It was shown before (2) that the parasitic larvae generally passed 

 outwaixls through the sides of the host caterpillar. More rarely one 

 finds larvae passing outwards on the dorsal surface, but no matter in 



