4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I40 



The order Geophilomorpha includes lo families and over 120 

 genera. Typically a long, vermiform arthropod, geophilomorphs are 

 found under rocks, in loose soil and forest litter, under the bark and 

 in the v^ood of decaying trees, and occasionally under drying dung 

 hills. They share with their chilopod relatives the outdoor life and 

 cryptozoic customs. The geophilomorphs have neither ocelli nor 

 Organs of Tomosvary. The antennae are the principal sense organs 

 of the head. The body tergites, unlike those of the other chilopod 

 orders, are homonymous. A single pair of mandibles, first and second 

 maxillae, comprise the mouth parts, which are in part concealed 

 by strongly developed prehensors. With the exception of the an- 

 terior and posterior extremities of the animals, the trunk is a repe- 

 tition of almost identical segments. Each body segment has its own 

 ganglion joined to its neighboring ganglia by paired connectives. The 

 ganglia and connectives comprise the ventral nerve cord. The alimen- 

 tary canal is a long continuous tube beginning at the mouth and end- 

 ing in an anal opening on the terminal body segment. A pair of Mal- 

 pighian tubules empties into the hind gut. There is a single elongate 

 testis in the male and paired seminal vesicles which communicate at 

 the single genital opening located ventrally on the penultimate seg- 

 ment. The female reproductive organs are similarly an unpaired 

 ovary, paired ducts, and a single opening situated on the penultimate 

 segment. 



Arthropod neuroanatomy. — Since the chilopod nervous system 

 follows the pattern of that of the typical arthropod, a brief review of 

 the structure of the brain and nerve cord will not be without profit. 



The neurons, the essential cellular components of nerve tissue, are 

 grouped together into masses called ganglia. The axons of these cells 

 emerge from the ganglia as nerves, or course within the ganglia as 

 fiber tracts. Other cells are present in the ganglia which are non- 

 nervous supporting elements. These are called neuroglial cells, or 

 simply neuroglia. The axons of invertebrates are generally considered 

 to be nonmedullated, but there is present a submicroscopic lipoprotein 

 sheath not unlike myelin. The central nervous system and the emerg- 

 ing nerves are clothed in a connective tissue covering composed of an 

 acellular "neural lamella" and a cellular "perilemma." The two are 

 referred to as "neurilemma." ^ 



of walking legs in all centipedes is never an even count. A tentative explanation 

 for intraspecific variation in the Geophilomorpha is that segments may be 

 added in successive molts and that variation in pedal counts may be a function 

 of age. (Crabill, private communication.) 



5 The term "neurilemma" is used differently by mammalian histologists. 



