and Position of the Hymenoptera. 93 
broad, transversely ovate, and not round, as if resulting from 
the fusion of two originally distinct ocelli. 
The antenne*, 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 maxilla and labial palpi and the antennary 
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 and 
Dana bave 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 
aminimum. 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 (Untersuchungen tiber die Entwickelung und den Bau der Glie- 
derthiere) and adopted by Claparéde (Recherches sur l’Hvolution des 
Araignées), that the antenne of the larvae are not homologous with those 
of the perfect insects, is untenable. In the larve of all Hymenoptera and 
numerous families of Lepidoptera and Neuroptera they are identical in 
position in all stages of development. 
