88 EMBRYOLOGY. 



ment of the insect lias gone on in all important 

 particulars mucli as in other insects, especially the 

 neuropterous Mystacides as described by Zaddach. The 

 head is longer vertically than horizontally, the frontal, 

 or clypeal region, is broad and greater in extent than 

 the epicranio-occipital region. The antennge are in- 

 serted high up on the head, next the ocelli, falling 

 down over the clypeal region. The clypeus, however, 

 is merged with the epicranium, and the usual suture 

 between them does not appear distinctly in after life, 

 though its place is seen in fig. 13 to be indicated by a 

 slight indentation. The labrum is distinctly defined 

 by a well-marked suture, and forms a squarish knob- 

 like protuberance, and in size is quite large compared 

 to the clypeus. From this time begins the process of 

 degradation, when the insect assumes its thysanurous 

 characters, which consist in an approach to the form 

 of the myriapodous head. The front, or clypeal region, 

 being reduced to a minimum, and the antennae and 

 eyes brought in closer proximity to the mouth than in 

 any other insects. 



" That other most essential thysanurous charac- 

 teristic, the spring, is now fully formed. It arises as 

 a thick tubercle from the sternite of the penultimate 

 segment of the abdomen, and subdivides into a pair of 

 two-jointed, finger-shaped prolongations. 



" The tip of the abdomen is deeply bilobate, the 

 median line of the body being deeply impressed. 



" The final stage in the life of the embryo is just 

 previous to hatching (figs. 14, 14 a). At this time the 

 animal lies with the body so curved that the tip of the 

 abdomen just touches the mouth. The ocelli are 

 situated on an irregular lunate spot. The mandibles 

 and maxillae are long, slender, blade-like, concealed 

 within the head, so that the mouth is somewhat tubular, 

 as it appears in a front view of the head. They move 

 back and forth upon one another, and, in their relation 

 to the head, may be compared with the base of the 

 mandibles and maxillte in the head of Cimex lectularms 



