416 



THE BIOLOGY OF MARINE ANIMALS 



depolarization proceeds over the plasma membrane. In nervous tissues 

 the universal properties of excitation and conduction are accentuated as 

 the primary activities of the nerve cell. 



Protozoa. Many ciliates possess a neuromotor system which is possibly 

 concerned with conduction and co-ordination of contractile responses. 

 This system consists of a regular network of fibrils, sometimes connected 

 with a region of differentiated cytoplasm known as the motorium, and 

 linking cirri, membranelles, etc. (Fig. 10.1). Destruction of the motorium 

 or interruption of the fibrils results in disturbances of locomotion and 



Motorium 



Cytosome 



Oral 

 ring 



Adora.1 

 ciliary 

 fibrils 



Nuclei 



Interciliaru 

 fibrils 



My one me 



Pharyngeal 

 fibril 



C ilium 



Basal 

 granule 



Fig. 10.1. Neuromotor System of a Ciliate Boveria teredinidi. 

 (From Pickard, 1927.) 



co-ordination of movement in ciliates (Euplotes, Chlamydodon, etc.). 

 Co-ordinated movements of cilia and other organelles depend upon some 

 integrating mechanism, and this may be the neuromotor system, as the 

 experiments just cited suggest (69, 110). 



Porifera. In sponges excitation is transmitted short distances in the 

 absence of nervous elements. The epithelial lining of the osculum consists 

 of spindle-shaped contractile cells (myocytes), forming a sphincter. These 

 cells respond directly to mechanical stimulation and cause the osculum to 

 close. Excitation resulting from tactile stimulation is transmitted short 

 distances (1-2 cm), but not from one osculum to another. Conduction 

 takes place from cell to cell (neuroid transmission) and is very slow (of 

 the order of a few mm/min in Stylotella) (85). 



