396 GEOLOGICAL SUEVEY OF THE TERRITOEIES. 



in the nerves, i. e., forming ganglionic enlargements, while there is a 

 marginal line nerve which connects the ends of the setal nerves. The 

 structure and arrangement of the nerves in the sixth eudite' of JEstJieria 

 appears to be nearly the same as in the BraneMpodidw, described far- 

 ther on, and the ganglion -cells are seen to be of the same size, the 

 parts being magnified with ^ Tolles A eye-piece. Plate XXIX, fig. 

 4, represents the end of the oviger of the same leg as fig. 7, Plate V. 

 A ganglion and setal nerve supply each seta, while the main nerve 

 passes through the middle, at tn, being reinforced by ganglion-cells ; 

 while at the end are several cells from which a nerve passes into each 

 seta. 



In EuUmnadia texana (Plate VII, fig. 2, 2a, 2&) where the fifth endite 

 of the first leg of the male is provided with a minute palpus-like pro- 

 cess, which was not observed in JEstheria, the histological structure of 

 the second joint is the same, though the nerve-fibers were not so dis- 

 tinct in the specimen examined ; EuUmnadia difiers, however, in the 

 terminal setse being coarser and much more numerous. 



In the Apodida^, from the nature of the dense opaque integument of the 

 appendages, it is i)robable that no special sense-apparatus is present. 



In the delicate swimming thoracic appendages of the Branchipodidae 

 some interesting histological features were observed, especially in legs 

 stained with carmine. 



In Branchipus vernalis the edges of the endites are provided with 

 clusters of two or three ganglion-cells which are situated in the mar- 

 gin near the insertion of the setse. These are noticeable in the fifth 

 endites, but especially so in the paddle-lilie sixth endite. (Plate XXX, 

 fig. 1.) This figure is drawn with the camera lucida and shows the 

 relation of the muscles supplying it, and also of the peculiar system of 

 ganglionic nerve-cells and nerves sujjplying the marginal ta(;tile setiie. 

 The striated muscular fibers are situated in the central portion of the 

 foot {muscle); they suddenly terminate in the manner indicated in the 

 figure, and originate from a median muscle passing out of the axis of 

 the limb; associated with them are irregular groups of ganglion-cells. 



The marginal ganglion-cells are arranged in two series: a submarginal 

 set [710^] and a marginal set (nd^). Whether the masses of parenchy- 

 matous matter filling the spaces between the two sets is truly nervous 

 matter, or undilferentiated protoplasm, I cannot say, but, judging by fig. 

 3, it is probably nervous. At the base of the anterior margin of the 

 endite where the setas are reduced in size the submarginal series of cells 

 disappear. Toward the posterior margin the setal nerves are seen to 

 enter the setse from a group of submarginal ganglion-cells. The con- 

 nection of the submarginal and marginal series of cells and nerves with 

 a main axial nerve of the leg was not observed, though several speci- 

 mens were examined and search made for it, and hence I am inclined 

 to think that the system of setal nerves and their cells is independent 

 of the central nerve system. 



In fig. 2 of the same plate is represented the sixth endite of one of 

 the anterior legs of IStreptocephahis texanus^ in which there is neaily the 

 same relation of parts as in Branchipus. The axial branches of the two 

 muscles (mus) are seen to be in one case connected with the series of 

 striated mus iles in the central area of the endite. No main endital 

 nerve was detected, and here, as in Branchipus, we see the same system 

 of submarginal and marginal nerve-cells, and of setal nerves. The cells, 

 however, are less numerous as seen in fig. 3, which represents the end of 

 a bundle of striated muscular fibers ; also their mode of termination, the 

 space between the ends of the muscular fibers, and the submarginal 



