134 Annals Entomological Society of America [Vol. XIII, 



SMALL LARGE 



Ratio, third to fourth antennal segment 1:1 2.9 : 1 



Ratio, third to fourth abdominal segment 1:1 1.5 : 1 



Number of intermediate teeth of mucro 1 8 



Number of teeth of unguis 1 4 to 6 



Intergradations in these respects occur in individuals inter- 

 mediate between these two extremes. This variation, occurring 

 during the growth of a single individual, is so extensive that 

 one who studied only one of the youngest and one of the oldest 

 specimens might easily mistake them for two distinct species. 

 (Schaffer.) 



In a few Collembola the number of antennal segments 

 increases after birth. Heteromurus, for example, is born with 

 four, but develops five by the division of the basal segment 

 into two. Orchesella has at first four, and finally six, by the 

 division of the two proximal segments. The fourth antennal 

 segment may become subsegmented after birth, as in Smin- 

 thurus and Heteromurus; and numerous subsegments develop 

 in the third and fourth segments in Tomocerus . 



The postembryonic changes in coloration in Collembola are 

 often striking. Collembola at hatching are usually white 

 (sometimes yellow), except for the black ocular pigment, 

 though most of them acquire pigments and color patterns later. 

 Anurida maritima at first white, becomes dark blue. Species of 

 Sir a at birth lack their characteristic color patterns. Calistella, 

 yellow at hatching, gradually develops its color pattern with 

 each molt, and completes its pattern with the seventh molt. 

 (Skorikow.) 



Our knowledge in regard to seasonal histories in Apterygota 

 is fragmentary. Campodea fragilis survives the winter and 

 has been kept alive several months in captivity., Machilis 

 maritima lives longer than one year, is sexually mature in 

 spring, and does not molt in winter but molts at frequent 

 intervals during the rest of the year. Lepisma saccharina is 

 like Machilis in these respects. (Oudemans.) 



Among Collembola, Achorutes armatus in Massachusetts has 

 three generations during the year, and possibly four, which 

 mature at intervals of about six weeks. Achorutes packardi 

 in Massachusetts has two broods, annually, the eggs being laid 

 late in April and hatching in about one month. This species 

 exhibits seasonal dimorphism; its variety dentatus laying 

 eggs that produce packardi. 



