LrrEKAKV NoTic'ics. - xxxi 



neuroglia. The ganglionic cells lack a true cell wall, but are surrounded 

 bj a sheath of connective-tissue fibres. These cells present various 

 shapes, two of which deserve special mention. One of these tjpes has 

 been called by the author "chromatic cells," the other "ganglionic 

 nuclei." The chromatic cells are small and unipolar, and are confined 

 to the sensory regions of the brain. The bodies of these cells are so 

 poorly supplied with protoplasm that a casual glance reveals nothing 

 but the densely stained nuclei. The higher the type of brain the more 

 numerous these cells become. Among the Myriopoda, these cells are 

 very abundant in the complicated brain of jf^ulus and Scntig'era^ while 

 they are absent from the rudimentary brain of (tcoPIiUks. Among the 

 AracJinida, they are abundant in the highly de\eloped optic lobes of the 

 LycosidcE and Plialangidie : in the less differentiated optic lobes of the 

 the Agaletiidce they are represented by faintly stained cells; while in 

 the rudimentary lobes of Pholcidcs they are replaced by cells of the 

 ordinary type. The ganglionic nuclei are small, granular; densely 

 stained nuclei are found in the brain of Sciitigeya. The nerves are 

 hollow tubes containing a liquid. The tubes passing entad penetrate 

 the brain and expand to form the sheaths of the ganglionic cells. The 

 neuroglia has a more delicate structure in sensory and psychical areas 

 than elsewhere. 



3. Alyi'iofodd. — The myriopod brain is constructed upon the same 

 plan as the insect brain; it consists of three ganglia homologous to those 

 that are found in the insect brain. Consequently there exists in the 

 myriopods three pre -oral somites homologous to the corresponding 

 somites of insects and crustaceans. 



The protocerebron (the ganglion of the first cephalic somite) is com- 

 posed of two portions, corresponding to similar divisions of the insect 

 brain. The lateral portions of the protocerebron constitute the optic 

 lobes, and are in direct communication with the eyes. The remaining 

 portion is psychical in function, and gives off a pair of nerves to the 

 organ of Tomosvary. 



The deutocerebroii (the ganglion of the second cephalic somite) is 

 composed of two antennary lobes, which are united by the antennary 

 commissure, and of an undifferentiated portion, corresponding respec- 

 tively to the olfactory and dorsal lobes of insects and crustaceans. 

 Except in 5^«/«.s-, where it is divided into an olfactory and probably a 

 motor fasciculus, the antennary nerve is a mixed nerve, as it is in the 

 insects and Crustacea. As in the insects and Crustacea, so here the 

 dorsal lobe gives origin to a small peripheral nerve (nerf tegumentaire), 

 and, as among the insects, it also gives origin to a pair of visceral nerves. 

 Consequently it is homologous to the first paired ganglia of the insects. 



The ti-itoccrehron (the ganglion of the third cephalic somite) corre- 

 sponds both to the tritocerebron and to the first visceral ganglion of 

 insects and Crustacea. According to Viallanes, the tritocerebron of the 

 Crustacea is composed of the following parts: Two antennary lobes, two 



