i;o INSECT TRANSFORMATION 



lustrous appearance as it runs and jumps rapidly and with 

 agility among the stones and rocks of the tidal margin. The 

 feelers on the head are long and many- jointed. Examining 

 the jaws we find that the mandibles (Fig. 97 A) differ from 

 those of any adult winged insect and resemble those of certain 

 Crustacea, having an elongate, tapering basal region, a central 

 ridged grinding area and a toothed apex, while the maxillulae 

 (Fig. 97 c) those minute appendages between the mandibles 

 and maxillae are quite well developed and hinged on to the 

 base of the tongue. Attached to the haunch of each thoracic 

 leg is a short un jointed stylet (Fig. 96 s), and similar structures 

 are found in pairs on each abdominal segment from the second 

 to the ninth inclusive, the hinder ones being relatively long. 

 The abdominal segments also carry curious little bladder-like 

 " exsertile vesicles ", and on the eighth and ninth segments 

 are paired " genital processes ", those of the female forming 

 the ovipositor (Fig. 96 o). The tenth abdominal segment 

 bears a pair of elongate many- jointed cerci (c), and a median 

 tail-filament (mf], of similar aspect to these, projects between 

 them from the tip of the abdomen. It will be realized that 

 such an insect differs from a grasshopper or beetle, not only on 

 account of the absence of wings, but by the possession of 

 crustacean mandibles, prominent maxillulae, and a series of 

 paired limbs on most of the abdominal segments. 



Some recent studies 1 of the life-history of such insects, 

 show that there are at least five stages before the adult con- 

 dition is reached, and that in the first two of these the young 

 insect is devoid of scaly covering, has no stylets on the 

 haunches of the legs and no trace of genital processes. In 

 the third stage scales are present and the haunch-stylets are 

 recognizable, though small, but the genital processes are still 

 wanting. These appear in the fourth period of the life-history, 

 but they are short, and, in the female, do not show the ringed 

 aspect which characterizes them in the developed ovipositor. 

 It is of great interest to be able to trace changes, that if not 

 very profound are markedly recognizable in the life-history 

 of these primitive wingless insects. In a specimen late in 



1 R. Heymons : " Ueber die ersten Jiigendformen von Machilis ". 

 Sitzgs. Gesellsch. naturforsch. Freundc, Berlin. 1906. K. W. Verhoeff : 

 " Ueber Felsenspringen, Machiloidea. Die schuppenlosen Entwicklung- 

 stufen". Zool. Am., XXXVIII. 1911. 



