and Position of the Hymenoptera. 93 



broad, transversely ovate, and not round, as if resulting from 

 the fusion of two originally distinct ocelli. 



The antennae*, by their form and position, naturally succeed 

 the labial palpi. Considering how invariably in the Crustacea 

 the eyes are situated in front of the gnathopods, we feel con- 

 vinced that the same position must be allowed them in the head 

 of insects. This will bring the ocelli most in advance of all the 

 other appendages. The bulk of the head of insects must, then, 

 be formed by the great expansion of the eye-pleurites, which, so 

 to speak, are drawn back like a hood over the basal rings, while 

 the rings bearing the maxillae and labial palpi and the autennary 

 ring are thrust out, telescope-like, through the large swollen 

 eye-ring; as in Decapods, a single ring covers in the aborted 

 ring composing the rest of the cephalothorax, as Edwards an4 

 Dana have shown, and our investigations have taught us., Thus 

 the upper surface of the head is composed of expansions of the 

 pleural pieces of the ideal arthromere, which never developes the 

 sternal nor probably the tergal portions in front of the mouth. 

 Thus each region of the insectean body is characterized by the 

 relative development of the three elements of the arthromere. 

 In the abdomen the upper (tergite) and under (sternite) surfaces 

 are most equally developed, while the pleural line is reduced to 

 a mniimum. In the thorax the pleural region is much more 

 developed, either quite as much as or often more than the upper 

 or tergal portion, while the sternite is reduced to a minimum. 

 In the head the pleurites form the main bulk of the region, the 

 sternites are reduced to a minimum, and the tergites are almost 

 entirely aborted, or may perhaps be identified in the centre of 

 the "occiput,^' or what is probably the mandibular (or mandible- 

 bearing) ring, and in the " clypeus." 



In the abdomen the same abolescence of parts strikingly 

 exemplifies what may be called the law of systolic growth, where 

 certain parts of the zoological elements of a body are in the 

 course of development either greatly enlarged over adjoining 

 parts or become wholly obsolete, as stated by Audouin and 

 St.Hilaire, who ascribed it to the principle of "arrest of deve- 

 lopment," which is now used by physiologists in a more limited 

 sense. While, as we have shown above, the genital armature of 

 insects is not homologous with the limbs, there are, however, 



* Repeated observations have taught us that the idea advanced by 

 Zaddach (Untetsuchungen iiber die Entwiekelung und den jBau der Ghe- 

 derthiere) and adopted by Claparede (Recherches sur I'Evolut.on des 

 Araignees), that the antennse of the larvaj are not homologous with those 

 of the perfect insects, is untenable. In the larvae of all Hymenoptera and 

 numerous families of Lepidoptera and Neuroptera they are identical in 

 position in all stages of development. 



