746 



SCIENCE. 



[X. S. Vol. XVIII. No. 407. 



some five weeks later, range from 534 to 

 2,080 mg., or 85 per cent, of the mode for 

 the lot. These embryonic but potentially 

 large variations have simply 'grown up' 

 along with the insect and are as truly eon- 

 genital in the adult as they were in the 

 newly hatched larva. This would seem to 

 place quite conclusively in the category of 

 congenital variations some part of those 

 variations (in size and propoi'tions of 

 parts) which are commonly, and properly 

 to some degree, called acquired. 



while the third lot was twenty-four hours 

 behind the second. All the individuals of 

 the first lot had finished moulting on April 

 20, all of the second on April 24, while the 

 moulting in the third lot continued until 

 April 29. 



As in the matter of weight, this retard- 

 ing of the functions, by means of a reduced 

 food sixpply, affects not only the immediate 

 generation which is subjected to the famine, 

 but the lingering etfeets of it may be traced 

 in the progeny of the dwarfed individuals 



3. That conditions of alimentation bear 

 a directive relation to functional activity 

 may be demonstrated by reference to the 

 records of the physiological functions of 

 moulting, spinning, pupating and emerging, 

 of the individuals of the experimental lots. 



An abnormal extension of the time 

 needed for the metamorphosis follows upon 

 a reduction of the food supply. The de- 

 gree of extension depends with the utmost 

 nicety upon the amount of food given the 

 larvas. For example, among the 1901 gen- 

 eration of silkworms, one control lot of 

 tM'enty larvas was given the optimum 

 amount of food, a second lot of twenty 

 larvffi one half this amount, and a third 

 lot of twenty larvaj one quarter of the 

 amount. To take the time of the fourth 

 moulting as an illustration, the moulting 

 was begun by the first lot, which led the 

 way by two and a half days, at the end 

 of which the second lot began to moult, 



at least unto the third generation, even 

 though two years of plenty follow the one 

 year of famine. The conditions which ob- 

 tain in each lot of individuals of the 1903 

 generation at spinning time are shown in 

 the accompanying table, which is based 

 upon polygons erected to include all the 

 individuals in each lot. 



This period in the life of the silkworms 

 is particularly advantageous for considera- 

 tion here because it marks the completion 

 of the feeding, so that the individuals of 

 under-fed ancestry have been given the best 

 chance to recover, while those subject to 

 altered food conditions have had the benefit 

 of the alteration during the entire food- 

 taking period of life. 



In the table '0' means optimum amount 

 of food and 'S' means short rations. To 

 the right of the history of the lots is a 

 section showing the rank of the lots as to 

 the extreme time limits of the spinning 



