382 HARRY H. CHARLTON 



related forms have been published. The writers, Claypole ('98), 

 on Anurida maritima, Lecaillon ('01), on Orchesella villosa, and 

 Willem ('00), on Podura aquatica, simply report isolated obser- 

 vations which are necessarily incomplete and limited to the class 

 Collembola. 



The Lepismatoidea have therefore never been made the sub- 

 ject of a cytological study, and it was in the hope that a survey 

 of this primitive form would throw some light on the present-day 

 cytological problems that this investigation was undertaken. 



The completion of the study shows that, instead of the expected 

 simplicity, the process actually is a complicated one, differing 

 only here and there from that already described in other forms. 

 These differences, however, are interesting and, together with 

 the fact that it is the first cytological work in a new class of 

 insects, warrant its presentation. 



The work was done at the Osborn Zoological Laboratory at 

 the suggestion of Professor Petrunkevitch beginning in the fall 

 of 1916. During 1917-19 it was practically suspended except 

 for an occasional day or so at Columbia University. It gives 

 me pleasure to express my thanks to Prof. E. B. Wilson for his 

 kindness in giving me laboratory privileges at Columbia and to 

 Prof. Frank R. Lillie for facilities accorded at the Marine Bio- 

 logical Laboratory, Woods Hole, Massachusetts, during the 

 summer of 1919. 



Most of all, I am indebted to Prof. Alexander Petrunkevitch, 

 first, for suggesting the problem and later for his unfailing help 

 and criticism. 



MATERIAL AND METHODS 



Lepisma domestica, commonly called the fire-brat, from its 

 frequently observed habit of running apparently unharmed over 

 hot stones in bakeries, belongs to the class Thysanura of the 

 order Lepismatoidea. It is a fairly common insect in New 

 Haven, and can be kept alive in the laboratory for a considerable 

 period. My method has been to keep them in large glass Stender 

 dishes without covers, since the insects cannot climb up a clean 

 glass wall, and to provide them with a cereal such as corn flakes 



