MISCELLANEOUS 



55 



purely heritable and cannot be increased by selection or hybridization, 

 and (b) that therefore it is an ontogenetic character but one not 

 produced by crowding. 



This conclusion seems quite opposed to that indicated by the state- 

 ments of Duseigneur, Lambert and others. But nevertheless they are 

 the only conclusions that can be derived from my data. 



If the data did not include records of the second generation pro- 

 duced from matings made to test the possibility of the double cocooning 

 habit as a Mendelian recessive, it might be assumed that this habit is 

 of such a recessive character, not appearing in the first generation be- 

 cause of the dominance of the lack of the habit. But the data for the 

 second generation although covering but few cases are unmistakable 

 and definite so far as they go and show clearly that there is no basis 

 for interpreting double cocooning behavior as a recessive character of 

 alternative inheritance. The percentages of doubles appearing in the 

 three second generation rearings are just about the percentages which 

 might be expected to appear in any rearing, and are far too low to 

 correspond to the expected percentage of a Mendelian recessive. 



Although the single fact that in all the hundreds of rearings made 

 in the laboratory in the last five years the spinning larvae had been 

 crowded in practically every case would indicate that the mere condition 

 of crowding is not sufficient stimulus to determine double cocooning, it 

 may be interesting to record the results of a few special experiments 

 tried on individual worms to test the effect of crowding. Several 

 times pairs of larvae which had begun to spin double cocoons were 

 separated and only very rarely in such cases was double cocooning 

 given up. That is to say, such would-be double cocooners after being 

 separated, in some cases 15 inches apart, would find their way to- 

 gether again and rebegin the double cocoon. In one case one of two 

 larvae which had begun a double cocoon together was removed and 

 another larva ready to spin was substituted for it. The result was a 

 desertion by both of the double cocoon already started and the spinning 

 of a single cocoon by each. At another time 14 larvae ready to spin 

 were arranged in couples and each couple put into a space which com- 

 pelled constant crowding of the two. Yet not one double cocoon was 

 produced. All of the larvae spun singles. Three larvae ready to spin 

 were introduced one into each of three nets already begun by three other 

 larvae. The result was six single cocoons, the introduced larvae 

 deserting the already begun net in each case. 



Miss McCracken has paid some special attention to the question 



