SPERMATOGENESIS OF PEDICULUS VESTIMENTI. 377 



and he proved to be a thoroughly dependable food supply. 

 He never missed his daily hour in my laboratory for the five 

 months I employed him. 



When feeding the lice I at first used the usual method of 

 putting a number in a tube, inverting the tube on the arm and 

 holding it securely in place to prevent the lice from escaping. 

 I found this method unsatisfactory for several reasons and 

 devised therefore quite a different technique. Lice cannot crawl 

 up a glass surface if it is clean and are therefore perfectly safe 

 in a glass ring even if it is only 2 cm. high. I had such rings 

 made to order and fastened them securely onto the arm with 

 melted paraffine. In this manner several different experiments 

 can be conducted at the same time and the generations can be 

 kept separate further the lice can be conveniently studied with 

 a lens during the hour they are feeding. For the remaining 

 twenty-three hours they were kept in a Pasteur incubator at a 

 temperature between 27 and 29 C. While in the incubator the 

 lice were kept in cages such as those used in the laboratory for 

 raising various insects. This cage is the tube de Borel, in which 

 is placed an inner tube for the insects, this being held in the 

 center by absorbent cotton which is kept wet to insure sufficient 

 moisture. I found the use of absorbent cotton very inconvenient 

 and replaced it with a short tube having an aperture large enough 

 to contain the inner tube and open at both ends with a lip at 

 each end sufficiently wide to center it in the tube de Borel. 

 The inner tube in which the insects are kept is dropped into this 

 shorter tube and an inch of water kept in the tube de Borel. 

 I found this method a great economy of time, for it was necessary 

 to pack the cotton around the inner tube with much care, since 

 if the opening came in contact with the inner surface of the tube 

 de Borel (often quite wet) a drop or two sometimes dripped into 

 the inner tube and cost the life of one or more nymphs. 



Several years of experience in crossing and raising other 

 species of Hemiptera have been my guide in raising the lice. 

 Miss Strobell and I found that the species we studied required 

 as much humidity as possible while avoiding any condensation 

 of the moisture. This I have found true for lice a half a drop 

 of water or less can kill a nymph. If he gets on his back on the 



