1920] Folsom: Apterygota 135 



The following data were sent to me from Arnprior, Ontario, 

 by Mr. Charles Macnamara, an exceptionally keen and thorough 

 observer : 



"Around here Achorutes socialis (the 'snow-flea') oviposits in 

 spring, and the mature individuals have disappeared completely by 

 June 1st. Well-grown individuals begin to appear again in September 

 and October, but the very largest usually (not always) are to be found 

 only in April and May. Apparently they grow all winter under the 

 snow. As an exception though, I fotmd some 2 mm. individuals (the 

 maximum size) in late October, on a white birch. 



"Eggs of Achorutes socialis hatch in 11 to 14 days, and in 9 to 10 

 weeks the young are .3 mm. to .5 mm. long, and fairly well pigmented. 

 Another spring layer is Onychiurus fimetarius; eggs of which laid May 2, 

 hatched May 22, period, 20 days. 



"In my vials in the house, Achorutes hunii and Neanur a niuscorum 

 both oviposited in the early winter. Eggs of A. humi laid November 

 15, hatched December 7, period, 22 days. Those of N. niuscorum laid 

 December 4, hatched January 8, period 35 days. Under natural con- 

 ditions outside, however, I doubt if the eggs of these two species would 

 have hatched until spring. 



"Specimens collected as well-grown adults survive in captivity 

 for very various periods. Sminthurus and Papirius in my hands are 

 always very short-lived — a few weeks at .most. Isotoma may live for a 

 couple of months, but the most resistant to captivity are Achorutes 

 socialis, 5 to 6 months; A. packardi, 7 months; and Xenylla maritima, 

 V2}/2 months. In estimating the length of life to these periods should 

 be added the age when captured, and of course that is unknown to me. 



"Achorutes socialis continues to grow long after it is sexually mature, 

 and keeps casting its skin as long as it lives." 



This is true of Collembola as a rule, which molt after growth 

 has ceased. The total number of molts has not been ascertained 

 in the case of any collembolan. Tomocerus plumbeus molts 

 throughout the year at intervals of two to three weeks. (Som- 

 mer.) In Tomocerus flavescens americanus the intervals between 

 successive molts increase with the age of the individual. Thus 

 the youngest specimens molt every two days, and old individ- 

 uals every six to eight days. 



It remains to summarize the significance of these facts as 

 follows: Apterygota at hatching are not structurally finished, 

 or complete; but undergo further development in respect to 

 various details of structure. 



The postemlpryonic development of pigmentation in Col- 

 lembola is (to judge from observations made on several genera) 

 the direct result of exposure to sunlight, and may; be prevented 



