289 [Packard. 



That there are seven such appendaires, among which we would iuckide 

 the eyes, which, if not homologous with the limbs, or more properly- 

 speaking, repetitions of the ideal appendage, are at least their equiv- 

 alents, in that they are situated on a distinct ring, as are the ocelli 

 which are exact equivalents or repetitions of the eye, is evident. 



The larvaj of Ephemera and Libellula, in the head of which these 

 parts of the cephalic rings by reason of the degradational character 

 of the insects appear in their simplest forms, aiford us the best mate- 

 rial for study. In the head of the larva of Libellula we have 

 observed that the greatly elongated labium, masking, when at rest, the 

 mandibles, is in reality composed of three sternites, immersed in, and 

 surrounded by three |j/eu/-i7e.'>, all bearing appendages, the basal pair 

 being the mandibles, the middle pair maxilla, and thirdly, the pair 

 of labial palpi, all of which are placed behind the mouth-opening. 

 Beyond, and in front of the mouth, are successively placed the 

 sensory organs; the antennse, the pair of eyes, and what we must con- 

 sider as two pairs of ocelli, since the early forms of Ephemera, and 

 the early stages of Bombus, show the three ocelli resting on three sep- 

 arate pieces ; the two posterior pieces (plexites) forming a pair, while 

 the single ocellus in advance is placed on a triangular piece, which 

 we consider as two pleurites united on the median line of the body, 

 as the ocellus has a double form, being broad, transversely ovate, and 

 not round, as if resulting from the fusion of two originally distinct 

 ocelli. 



The antennaj* 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 convinced 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 expan- 

 sion of the eye-pleurites, which, so to speak, are drawn back like a 

 hood over the basal rings, while the rings bearing the maxilla3 and la- 

 bial 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 rings composing the rest of the cephalo-thorax, as Edwards 

 and Dana have shown, and our own 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 develops the sternal, 



♦Repeated observations have taught us tliat the idea advanced by Zaddach (Un- 

 tersuchungen iiber dieEntwickehmg und den liau der Gliederthiere), and adoi)ted 

 by Claparede (Recherches sur I'Evolution des Araign^es), that the antenna; of the 

 larvas are not homologous with those of the perfect insects, is untenable. In the 

 larva of all hymenoptera and numerous fomilies of Lepidoptera and Neuroptera, 

 they are identical in position in all stages of development. 



P&OCEEDINGS B. S. N. H.— VOL. X- 19 MAY, 1S(J6. 



