Introduction to Animal Morphology. 23 



Crustacea the nerves have medullary sheaths. When 

 nerves divide, their sheaths attenuate, but the sheath 

 on small branches is thicker than on larger. On very- 

 small branches the sheath of Schwann is lost first, then 

 the medullary sheath : then the axis cylinder splits 

 into its component fibrils. 



Nerve fibres begin in uni- or multipolar,* finely granular, 

 nucleated, and nucleolated nerve corpuscles (dilatations of the 

 axis cylinders ?) surrounded by a capsule of connective tissue. 

 Clusters of nerve cells embedded in protoplasm and a copious 

 inter-fibrillar matrix are called ganglia. Nerves end in diffe- 

 rent ways : — i . In free ends between epithelial cells (in cornea, 

 Hoyer and Cohnhewi). 2. In pear-shaped bodies (epiglottis, 

 Klein) or pyramids of protoplasm with clear elliptic nuclei 

 (testis, Zf/zmc/2), or in branched gland-cells (?)(-^M^<?r). 3. In 

 sense organs they end in fusiform or rodlike bodies with non- 

 vibratile blunt processes (gustatory cells of Lovhi and Key^ 

 the smelling cells of Schultze, sentient cells of rete mucosum, 

 Tomsa, retinal cones, and Cortian rods). 4. In Pacinian cor- 

 puscles, or dilated bulbs of diverging primitive fascicles sur- 

 rounded by a finely granular mass of protoplasm, and en- 

 closed in dense concentric laminae of connective tissue.f 

 Similar club-shaped bodies without the connective capsule 

 are the end organs of Krause. The corpuscles of Meissner in 

 the sensitive palmar papillae, are furrowed bodies into which 

 a nerve enters and twines round once or twice, rising to its 

 top. 5. In muscle, nerve fibres end by entering the sarco- 

 lemma in little conical eminences {Doyerian papillae), then 

 breaking up into a wide-meshed plexus of fine filaments which 

 may end in a plate composed of an upper granular layer and 



* Each cell may have many poles, but has only one peripheric branch 

 (Deiters). Sometimes a spiral filament (or 2, 3, or 4 such, as in the Frog) 

 winds round the straight peripheric branch — two kinds of these, nervous 

 from the substance of the corpuscle, fibrous from a basal network, are 

 described by Schwalbe. 



t Bodies like Pacinian corpuscles, arranged in chains on an axis band, 

 exist in the tympanum between the pyramid and the canal for the tensor 

 ■ tympani muscle, as well as in the mastoid cells. 



