NO. 14 INSECT ABDOMEN SNODGRASS 69 



nation may take place by the emission of a drop of spermatic fluid 

 from the male, which, falling to the ground, is taken up directly by 

 the female into her genital orifice. There seems to be little doubt that 

 the mating performance of the Sminthuridae is accessory to insemina- 

 tion, since Falkenhan finds that the eggs of females that have not 

 been allowed to mate are infertile. Egg laying takes place ordinarily 

 about 14 to 18 days after mating, though the time varies according to 

 temperature and the age of the female. 



The Protura, in the fully matured stage, have 12 abdominal seg- 

 ments, and this character would appear to relate them more closely 

 to insects other than Collembola, in which the maximum segmenta- 

 tion of the abdomen, as shown in the embryos of some forms, consists 

 of eleven somites and a telson. The Protura dififer from other hexa- 

 pods in that the last two somites before the end segment, or telson, 

 are formed during postembryonic growth, as in anamorphic Chi- 

 lopoda. Whether segmentation is completed before or after hatching, 

 however, cannot be a matter of great importance, since it is variable 

 among the chilopods themselves. The genital openings of the Protura 

 are on the penultimate body segment as in Collembola and Chilopoda, 

 but, as already pointed out, the genital segment, though subterminal 

 in position, is numerically quite a dififerent somite in each of these 

 three groups. 



The gonads of Protura lie ventral to the alimentary canal, as in 

 Collembola, but in their structure they resemble a single gonadial 

 tube of an insect ovary or testis of the usual compound type, in which 

 each tube has a germarial zone at its apex. The proturan ovary or 

 testis, as described by Berlese (1910), is a large tubular sac with the 

 tapering anterior end folded ventrally and posteriorly. In the deflexed 

 apical region are contained the oogonia or spermatogonia, and the 

 rest of the tube is occupied by the developing oocytes or spermatocytes. 

 The oocytes are arranged in a single series ending with a mature ovum 

 as in an ovariole of other insects, and the successive stages of the 

 maturing spermatozoa form zones of growth as in an ordinary sperm 

 tube. The proturan gonad thus does not have the primitive or gener- 

 alized structure of a collembolan or chilopod gonad, and its simplicity 

 of form, therefore, would appear to be the result of elimination of 

 tubes from a compound organ, as is probably the case also in certain 

 Diplura in which the gonad consists likewise of a single egg tube or 

 sperm tube. The vasa deferentia of Protura discharge individually 

 through terminal ejaculatory ducts, but the oviducts come together 

 in a short median outlet tube. 



