922 



INSECTA. 



of the organs of generation, are retractile within 

 the abdomen. The sixth segment is concealed, 

 and the seventh and eighth segments, particu- 

 larly the latter, which is greatly enlarged, form 

 the chief portion of the abdomen. In the 

 common honey-bee there appear at first to be 

 but five segments ; but one segment, the sixth, 

 which forms the base of the abdomen, is almost 

 concealed, and the others constitute the sting 

 and retractile organs of generation. In the 

 male or drone two segments are lost in the 

 termination of the male organs of generation. 

 Thus, then, the actual number of the segments 

 is the same in all Hymenoptera, the apparent 

 difference being occasioned by the retraction of 

 one or more segments within those which pre- 

 cede them. To so great an extent is this car- 

 ried in some species, as in the Chrysidida, that 

 the abdomen at first sight appears to be formed 

 of only four segments, the margin of the posterior 

 being armed with several spines. But even in 

 this family the number of segments is exactly 

 the same as in the Ichneumon above noticed, 

 in which all the segments are apparent. The 

 five last segments are retractile within the 

 abdomen, and when extended form a long 

 jointed tube, which is employed by the insect 

 for the purposes of oviposition. Thus then 

 the ovipositor of the Tubulifera, the sheath of 

 the sting in the Aculeata, and that of the terebra 

 or borer in the Terebrantia, are all derived 

 from the terminal segments of the body. But 

 we have already seen that in the hymenopterous 

 larva there is an additional segment to the 

 body, which from the existence of an appa- 

 rently additional organ in the perfect insect, 

 may reasonably be supposed to be especially 

 connected with the developement of that part. 

 On examination, however, it is discovered that 

 it is not from the fourteenth or terminal seg- 

 ment that the ovipositor, or sting, is entirely 

 derived, but from at least the two last segments, 

 the sheath being developed from elongated 

 portions of the thirteenth or penultimate seg- 

 ment, while the fourteenth forms only a short 

 valve at its base, like the extremity of the 

 abdomen in Sirex. From these circumstances 

 it is evident that the defensive organs of the 

 aculeate Hymenoptera are simply developments 

 of certain parts only of the sides of the abdominal 

 segments, while the tubulated joints of the ovi- 

 positor of the Chrysidida, with which there are 

 many analogies among the Lepidoptera, are the 

 entire segments. It is evident also that al- 

 though the fourteenth segment is certainly con- 

 nected with the sting or borer, it does not 

 become its chief part, the sheath of the organ 

 being always formed by parts of the thirteenth 

 and sometimes also of the twelfth segment, so 

 that these organs are simply developements of 

 parts which already exist in all insects. The 

 analogues of the ovipositor are found in the 

 Panorpida among the Neuroptera, and in the 

 Bombyad< among the Lepidoptera; while 

 those of the other forms of the same part, the 

 terebra and sting, exist in the exserted oviposi- 

 tors of the female Gryllid* in the Orthoptera, 

 and in the prehensile ones of some of the 

 Arciiida and other species, in almost every 



instance the parts being derived from similar 

 segments. 



In Lepidoptera the size of the three segments 

 of the thorax is more unequal than in Hymen- 

 optera. The prothorax is reduced to a very thin 

 plate or ring, more especially on its upper sur- 

 face or pronotum. On the prosternal surface 

 the primary parts, although greatly reduced in 

 size, are still distinguishable. The prostemurn 

 is a small square piece, which is articulated in 

 front by suture with a part of the anterior of 

 the basal joint of the first pair of legs, and 

 which we are inclined to regard as the tro~ 

 chantinus (Jig- 392, 2 /c). Immediately above 

 this is a short semicircular piece, which is 

 perhaps the analogue of the epimeron, and 

 which is united by suture to a large broad 

 lunated piece, that forms the greater part of 

 the lateral surface of the prothorax, and is con- 

 tinuous with the narrow ring on the upper sur- 

 face (Jigs. 391 , 392, 2). The meso-notum is enor- 

 mously developed. The pr&scut um (Jig. 391) 



Fig. 391. 



J3 



Dorsal surface of Sphinx ligustri. 



is hidden within the segment and forms the pro- 

 phragma, the anterior boundary of the segment. 

 Laterally it is extended on each side beneath 

 the scutum as far as the anterior boundary of 

 the wings, where it is developed on each side 



