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HANDBOOK OF INVERTEBRATE ZOOLOGY. 



per cent alcohol until they are wanted. They should 

 then be placed in absolute alcohol for ten or twelve hours, 

 after which they may be mounted in paraffine, as described 

 in Section VII. A series of thin sections through the 

 head should then be made and mounted in balsam for 

 microscopic examination. 



a. In a section through the anterior end of the head, 

 notice : — 



1. The cut surfaces of the five pairs of arms (Fig. 

 180, a, a, a, a, a). 



2. Near the centre of each arm a brachial ganglia (Fig. 

 186, b, b, b, b, b), which consists of a central axis of 

 wdiite matter or nerve fibres, surrounded by a layer of 

 gray matter or ganglion cells, outside of which the gan- 

 glion is covered by an investing 



d^ yt"^^--^ ^^ sheath. 



Fig. 185. — Diagram of vertical sec- 

 tion of buccal body. (Drawn from na- 

 ture by W. K. Brooks. ) 



a-b. The plane of the section shown 

 in Fig. 186. c-d. The plane of the sec- 

 tion shown in Fig. 187. c. OEsophagus. 

 d. Superior or ventral mandible, e. In- 

 ferior or dorsal mandible. /. Muscles 

 of dorsal mandible. g. Muscles of 

 ventral mandible, i. Tongue, k. Ra- 

 dula. ~ 



Fig. 185. 



3. In some of the sections, the transverse or circular 

 commissure, which connects these ganglia with each other, 

 will be found. Notice that the fibres of the commissure 

 pass through the layer of gray matter into the central axis 

 of white matter of the ganglia. 



4. In the centre of the section notice a large oval body, 

 the transverse section of the buccal mass. 



