COMPAEATIVE MOEPHOLOGY OF THE GALEODID.^. 345 



escape observation among the connective tissue. Further research is much needed. In the meantime, 

 perhaps, we are not wrong in assuming that the great nerve-mass in the brain, behind the optic ganglia 

 (which shows as a crescent in horizontal sections of Spiders, behind and half encircling the optic 

 lobes), would be the "sympathetic" ganglionic centre. 



The nerves of Galeodes are always in very close association with tracheae, a fact 

 which is interesting in connection with the close association of the nerves with the 

 blood-jmssages in Scorpio. 



Histology. — One observation seems to be worth recording. The cross-sections of the 

 large nerve-trunks show the usual fine network which represents so many tubes cut 

 across. But, in other parts of the body, where nerve-fibres can be seen isolated, they 

 are exquisitely fine fibrils with fusiform nuclei (PI. XXXII. fig. 7). These are most 

 easily seen in the racquet-organs (fig. 1, nf), but can be found also in other parts of the 

 body. What, then, are the tubes ? I would like to suggest the following explanation. 

 In order to protect the nerve-fibrils from mechanical stimuli along their courses, they 

 run in a delicate connective-tissue framework (comparable to that which envelops the 

 muscle-fibrils, PI. XXX. fig. 12). The hollow tubes are filled with fluid, and the fibrils 

 run along closely applied to their walls, the whole arrangement being an adaptation to 

 protect the nerve from mechanical stimulus of any kind along its course. In the 

 racquet-organs the fibrils are in no such danger ; they are enclosed, at least in the shaft, 

 in a stout cylinder of chitin, and run singly to their destinations. An examination of 

 the points of departure of large nerve-trunks from the brain leaves little doubt that the 

 tubes, which are at this point very large and irregular, are not the nerves themselves. 

 The fibrils themselves are, as a rule, too fine to be distinguished in the walls of the 

 tube, but their fusiform nuclei are often quite distinct. 



I have found the same nerve-fibrils in Scorpio., but have been unable to demonstrate 

 the individual nerve-fibrils in Spiders. An examination of the general structure of the 

 nerve-strands as they leave tlie brain, however, leaves little doubt in my mind that the 

 irregular tubes are but fluid-channels in the walls of which the — as a ru.le invisible — 

 nerve-fibrils run. The absolute necessity of isolating the fibrils in their courses from 

 the periphery to the brain seems certainly to require some such arrangement. 



VII. The Sense Organs. 



The Galeodidae, which are for the most part great hunters, are well provided with 

 sense organs. 



We have to describe (1) the large median eyes, (2) the vestigial lateral eyes, (3) the 

 protrusible organ at the tij)s of the pedij^alps, (4) the racquet-organs on the last pair of 

 legs, (5) sensory setae, (6) certain specialized areas containing organs of unknown 

 significance, presumed to be sensory. 



(1) The Median Eyes. — The large pair of median eyes stand on a tubercle anteriorly 

 in the dorsal suture, between the cephalic lobes. This tubercle, as we have seen, is 

 probably the remains of the original dorsal surface {cf. p. 310). 



The lenses are round glassy prominences. In the genus Galeodes they are very large 



SECOND SERIES. — ZOOLOGY, VOL. VI. 46 



