694 



SCIENCE. 



[N. S. Vol. XVIIT. No. 405. 



pei-manently, I prevented the issiiing of the 

 swarm until the ecstasy was passed and the 

 usual quietly busy life of the hive was re- 

 sumed. About three hours later there was a 

 similar performance and failure to issue from 

 the quickly un jacketed hive. On the next 

 day another attempt to swarm was made, and 

 after nearly an hour of struggling and mov- 

 ing up and down, depending on my manipula- 

 tion of the black jacket, most of the bees got 

 out of the hive's opening and the swarming 

 came off on a weed bunch near the laboratory. 

 That the issuance from the hive at swarming 

 time depends upon a sudden extra-development 

 of positive heliotropism seems obvious. The 

 ecstasy conies and the bees crowd for the one 

 spot of light in the normal hive, namely, the 

 entrance opening. But when the covering 

 jacket is lifted and the light comes strongly 

 in from above — my hive was under a skylight 

 — they rush toward the top, that is, toward 

 the light. Jacket on and light shut off from 

 above, down they rush; jacket off and light 

 stronger from above than below and they re- 

 spond like iron filings in front of an electro- 

 magnet which has its current suddenly turned 

 on. "What produces the sudden strong helio- 

 tropism just as the swarming ecstasy comes 

 on? That is beyond my observation. 



Dr. Loeb tells me that he has observed and 

 recorded a strong positive heliotropism in the 

 winged male and female ants at mating time. 

 They rush from their underground nest and 

 take wing directly toward the strongest light. 

 With both bees and ants this flying toward 

 the light at swarming and mating time, re- 

 spectively, has obvious advantages. It keeps 

 the swarm together and it takes them away 

 from the old community. Swarming and 

 mating flights are distribution and migration 

 of the species to new ground where are food 

 and space unneeded by the old community. 



During the last three years I have, with a 

 student, Mrs. Bell, been rearing siEvworms 

 under quantitatively determined varied condi- 

 tions of food supply, in an attempt to deter- 

 mine, also quantitatively, the extent and char- 

 acter of the induced variations. In these 

 experiments silkworms separated into various 

 lots (the individuals in each lot kept also 



apart so that each may get its rightful share 

 of food) are variously fed through their life 

 on an optimum of food, on one half optimiun 

 and on a minimum amount, that is, one which 

 will just keep the worms alive, developing and 

 growing. As the optimum amount is that 

 which permits the larvse to feed almost con- 

 tinuously, and as each under-fed worm eats 

 up as rapidly as possible its full supply, it 

 is evident that the half-fed and minimum-fed 

 worms have to spend long hours of non-feed- 

 ing, rest and quiet and — if it may be — medita- 

 tion. Now such a period of non-feeding and 

 inactivity is precisely a normal pre-molting 

 phenomenon of all sillcworms — and of other 

 lepidopterous larvEe, too, for that matter. 

 With this in mind it is interesting to note 

 that a common phenomenon in the life of the 

 under-fed worms was an abnormal increase 

 in moltings; that instead of adhering to the 

 time-honored and Bombyx-approved habit of 

 molting four times (exclusive of pupation) 

 during the larval life, most of these half- 

 starved larviE, with artificially imposed re- 

 peated periods of non-feeding, molted five 

 and a few even six times. It may be expected 

 that such a sapping of vitality as these starva- 

 tion rations must have produced would result 

 in a lessening of the physiological activity, 

 and a giving up of one or more meltings 

 rather than an increase in the number of 

 these betrayals of growing pains. But no, 

 there are more rather than fewer molt- 

 ings. Now in actual molting, the loosening 

 from the body of the old cuticle results from 

 the secretion by skin glands of a so-called 

 molting fluid; this secretion occurs during 

 the non-feeding resting stage normally im- 

 mediately preceding the molting. , Can the 

 abnormally induced non-feeding, inactive 

 periods imposed on the under-fed worms have 

 been the sufficient stimulus for setting up 

 this secretion and accumulation of the molt- 

 ing fluid resulting, as usual, in a loosening of 

 the cuticle? That is, do lepidopterous larvae 

 molt not just because molting is needed at 

 some particular time but because the cuticle 

 gets pushed off by a fluid which gets formed 

 and excreted whenever the larva stops feeding? 

 Of course the insect that wisely times its non- 



