24 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I40 



arthropods. They are located near the receptors in the epidermis. 

 The cell bodies located in the cephalic nervous system of bipuncticeps 

 fall into three categories : motor neurons, internuncial, or associational 

 neurons, and neuroglial (supporting) cells. 



The motor neurons are typically pyriform, unipolar nerve cells 

 which are rich in cytoplasm. A moderate amount of chromatin is 

 present in the nucleus. The single "stalk" or cell process usually 

 projects radially inward into the neuropile. The main process gives off 

 a collateral in the neuropile but continues uninterrupted to the effector 

 which it innervates. The collateral makes numerous connections with 

 the other elements in the neuropile and cortex, principally with the 

 associational components. 



The majority of cells found in the cortex of the brain are associa- 

 tion neurons. They are usually smaller than the motor neurons, and 

 their spherical nuclei are heavily stained in silver preparations. In 

 certain areas of the brain, particularly in the posterior cortex, these 

 cells are so crowded together that their nuclear membranes appear 

 to be touching. Very little cytoplasm surrounding a dark spherical 

 nucleus usually identifies the cell body as an associational neuron. 



Typical neurosecretory neurons were not observed in the frontal 

 lobes or in any other part of the supraesophageal ganglion with the 

 stains employed. In the subesophageal ganglion, however, four large 

 cells were discovered which may have neuroglandular significance. 

 The main center of neurosecretory activity has been found to be 

 located in this ganglion in a number of arthropods (Scharrer, 1941). 

 In bipuncticeps these large cells occur 70 to 100 micra posterior to 

 the anterior limit of this ganghon. They are ventrally situated on 

 either side of the midsagittal plane (fig. 3 indicated by x's.). 



The cells are pyriform and unipolar and have a large amount of 

 cytoplasm. The single stalk is directed dorsad and enters the neuro- 

 pile. Their dimensions are approximately 12X20 micra. The nucleus 

 is ellipsoidal and measures 5.7 X 6.9 micra. A dark, spherical nucleolus 

 about 1.5 micra in diameter is present and is eccentric in position (pi. 

 5, fig. 3). These cells are probably the largest found in the nervous 

 system of bipuncticeps and are considered "giant cells." 



In addition to the neuronal cells located in the cortex, neuroglial 

 cells occur. These may be found in the neuropile as well as in the 

 cortical layer. They have already been described. 



An abundance of tracheoles and tracheal fibers penetrate the neural 

 substance. These have been mentioned for two reasons: (i) They 

 are easily mistaken for nerve fibers in some "unsuccessful" silver 

 impregnations; (2) they are accompanied by elongate and flattened 



