MOEPHOLOGT OF BEAIN AND SENSE ORGANS OF LIMULUS. 41 



terminates in canals near the outer surface of the cuticula. 

 These sensory buds are distributed over the whole body, but 

 they are much more abundant in some places than in others. 

 They are as a rule innervated by delicate branches from an 

 everywhere present subdermal nerve-plexus, which is itself 

 connected with branches of the tegumentary nerves; but special 

 aggregations of buds may be supplied by special nerves, such as 

 the olfactory buds, and the gustatory cells and buds of the 

 mandibles ; both sets of the latter organs being supplied by 

 the two branches of the mandibular nerve (coxal nerve of 

 scorpions, supra-branchial nerve of Vertebrates). 



All these sense buds or sense cells in Limulus multiply 

 by division. This process is easily studied in the buds of 

 the inner mandibles, and in the gustatory cells of the man- 

 dibular spines. The division begins at the summit of a 

 cuticular canal, and gradually extends down into the organ, 

 the process being the same in both sense cells and sense buds. 

 The chitinous tubule itself does not divide ; a new one is 

 formed alongside of the old one ; a longitudinal constriction 

 then appears at the summit of the old cuticular canal, dividing 

 it into two diverging arms, the separation of which gradually 

 progresses toward either the sense buds or cells, as the case 

 may be. I do not know how the latter divide. 



There are at least five varieties of these two types that can 

 be recognised by their termination at the surface. (1) The 

 olfactory buds are connected with nearly straight canals, which 

 contract near the top into a very narrow slit (fig, 12, e and/). 

 (2) The gustatory buds of the inner mandibles are connected 

 with straight canals, resembling the ones just described, except 

 that they open out by excessively small pores (fig. 12, a, b, and c). 

 Just before reaching the surface the tubule expands into an 

 irregular, spindle-shaped body ; beyond this it becomes 

 extremely small, but still it can be followed with certainty to 

 the outer surface, where it terminates in a very shallow de- 

 pression (fig. 12, a). A dark coagulum of some kind usually 

 fills the cuticular canal, and completely surrounds the chitinous 

 tubule. (3) The buds scattered over the surface of the man- 



