ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 973 



branches, each ensheathed by long cells with relatively small nuclei 

 and large nucleoli. Each nerve ends in a ganglion of small cells 

 with round nuclei. This lies, for the most part, in the seventh joint. 

 Entering the ganglion the nerve divides into fibres, distributed 

 among the cells ; fine fibres pass anteriorly into the cones. The four 

 ganglia are closely approximated. The large cells ensheathing the 

 nerve below the ganglion were identified by Sazepin as ganglion cells. 

 Von Eath gives reasons against this view, and regards them rather as 

 fatty cells. He believes that in the ganglion the fine nerve-fibres 

 come into connection with the " ganglion cells," and that from 

 these, fine processes are given off to the cones. Each fibre would 

 be composed of the processes of a row of these sensory cells, and 

 each cone receives a number of fibres. Each ganglion exhibits 

 peripherally a peculiar dark-coloured strand, with very numerous, 

 deeply stained nuclei, but its nature has not been certainly determined. 



(6) The knobs. — The anterior margin of the seventh, sixth, and 

 usually also of the fifth joint, bear more or less cylindrical rods, 

 without an apical aperture. These knobs have corresponding ganglia, 

 which lie close to the hypodermis and almost imbedded in it. A 

 side branch is given off from the main nerve at the fifth and at the 

 sixth joint, and the ganglia associated with the knobs resemble those 

 of the cones. 



II. Sense-organs of the lower lip. — The anterior margin of the 

 lower lip usually exhibits two chitinous cup-shaped cylinders. The 

 floor of the cup, generally formed of a somewhat thin membrane, bears 

 a large number of cones, perforated at the apex. They are smaller, 

 longer, and more slender than the antennary cones. A fine hair-like 

 structure sometimes protrudes from the terminal aperture. Similar 

 organs occur on the so-called lobus lingualis of the lower lip. The 

 dorsal surface of this cap-shaped process bears a plate beset with 

 cones, and also another smaller plate directed forwards. These 

 sensory organs of the lower lip have not been previously recognized. 



From the lateral and inferior surface of the sub-cesojmageal 

 ganglion two nerves arise ; each divides into two branches, of which 

 the median leads to the sensory organs of the cap-like process, and 

 the more lateral again divides and supplies the lip-organs first 

 described. The ganglionic arrangements do not differ markedly from 

 those described in connection with the antennary organs. The same 

 sensory and ensheathed cells are to be noted. Herr von Rath regards 

 both sensory cells and supporting cells as resulting from modified 

 hypoderrnis. He does not discuss the exact function of the organs. 



5. Arachnida. 



Nerve-centres of Arachnids.* — M. G. St.-Eemy finds that the 

 brain in Tegenaria domestica, Epeira diadema, and Phalangium opilio 

 is formed on the same plan as in Scorpio.^ There are two sorts of 

 nerve-cells : (a) those with a distinct layer of protoplasm around the 

 nucleus ; and (b) those in which the amount of protoplasm is so small 



* Comptes Rendus, ciii. (1886) pp. 525-7. f See this Journal, ante, p. 791. 



