22 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I40 



portion of the oral opening. A nerve to the hypopharynx (N19) de- 

 scribed in 6^. hirsutipes by Fahlander was not observed in hipuncticeps. 

 Neither did N20 exchange fibers with its fellow of the opposite side. 

 A free tritocerebral commissure, therefore, does not appear in 

 hipuncticeps. 



The unpaired recurrent nerve N14, emerges 50 micra caudal to the 

 roots of N20. The recurrent nerve is dorsal to and runs between the 

 levator pharyngis muscles which insert on the pharynx (pi. 4, figs. 

 1-3). On each side of this nerve the labral nerve, N17, is observed. 

 These three nerves and a pair of tracheoles emerge simultaneously 

 from the ventral surface and form a "sort of tuft." This expression 

 was used by Saint Remy (1887) in describing the same site in 

 N ecrophloeophagus longicornis. The recurrent nerve continues 

 caudad for about 100 micra and bends sharply dorsad onto the 

 esophagus (fig. 3). The nerve then branches into two nerves on 

 the dorsal surface of the esophagus. They were not traced beyond 

 the point of bifurcation. 



4. Nerves of the suhesophageal ganglion. — Three pairs of nerves 

 emerge from the lateroventral aspect of the suhesophageal ganglion. 

 The mandibular nerve (fig. 2, NMD) emerges anteriorly. It is closely 

 followed by the nerve to the first maxilla (NMXi). The nerve to 

 the second maxilla (NMX2) emerges from the ganglion posteriorly. 

 In hipuncticeps the nerves to the first and to the second maxillae are 

 widely separated. The three nerves are sensory to the receptors and 

 motor to the intrinsic muscles of the mouth parts. 



HISTOLOGY OF THE CEPHALIC NERVOUS SYSTEM 



The histology of the nervous system of hipuncticeps is typically 

 arthropod in appearance. The ganglia and the nerves outside of the 

 ganglia are covered with a connective tissue sheath called neurilemma. 

 The neurilemma of the ganglia was previously thought to have the 

 same construction as that enveloping the peripheral nerves and con- 

 nectives. Recent studies, however, reveal that the nerves have a con- 

 nective tissue layer and a Schwann cell layer, while the ganglia have 

 a thicker connective tissue layer, a perilemmal cellular layer, and 

 neuroglial cells (Hess, 1958). 



I. Neurilemma and neuroglia. — The neurilemma is composed of an 

 outer homogeneous covering called the neural lamella, and an inner 

 cellular layer called the perilemma. This neurilemma may vary in 

 thickness within the same species. In hipuncticeps the ventral surface 

 of the brain has a thicker neurilemma than the dorsal surface. It may 

 vary from about 2 to 8 micra in thickness. 



