37^ HANDBOOK OF PHYSIOLOGY ^ NEUROPHYSIOLOGY I 



Fig3 



FIG. 3. Primary sense cells from the tentacles of the sea anemone Ceriantlms. [From Hanstrom (50).] 

 PIG. 4. Primary sense cells from the epithelium of the earthworm Lumbrkus. [From Hanstrom (50).] 

 FIG. 5. Bipolar sensory neurons from the skin of the slug Anon ater. [From Plate (9^).] 



FIG. 6. Various types of scolopophorous sense cells (scolo- 

 pidia) from the chordotonal organs of insects, a and h, am- 

 phinematic scolopidia; f, d, e, and/, mononematic scolopidia. 

 a, simple chordotonal organ; b, scolopidium from the haltere 

 of a muscid (fly); c and d, scolopidia from the tympanal organ 

 of the cicada Cicadetta coriaria; e, scolopidium from the tympanal 

 organ and /, from the subgenual organ of the grasshopper 

 Decticus. af, axial fiber; ch, chitin cuticle; dc, cap cell; ec, en- 

 veloping cell; hy, hypodermis; li, ligament; sc, sense cell; 

 si, scolops (apical body of the sense cell); tf, terminal strand of 

 the sense cell; and va, vacuole. [From Weber (137).] 



Some single sense cells show a further anatomical 

 differentiation. They have several short ramified fibers 

 (dendrites) which lead to auxiliary cells. E.xamples of 

 these are the stretch receptors at the joints in crusta- 

 ceans (i, 5). As a rule, the stretch receptors send a 

 fixed number of dendrites to a small bundle of muscle 

 fibers (fig. 15). 



The epithelial sense cells may be located in groups 

 and thus form anything from primitive to highly 

 specialized sense organs. If they are located in the 

 epithelium, they may often carry fine hairs on their 

 surface. Specific structures are often found in the 

 sense cells; the most complicated of such intracellular 

 structures are the apical bodies (scolopidia) in the 

 chordotonal and tympanal organs (35) diagrammed in 

 figure 6 and the rhabdomeres in the eyes of the in- 

 sects (39, 47). 



Some sense organs of invertebrates contain, side by 

 side, sense cells which are morphologically differen- 

 tiated in different degrees. An example is the sense 

 cone on the last joint of the antennae of the Diplopoda; 

 in this three different types of sense cells are located 

 closely together (fig. 7). 



The sense cells of an organ may be morphologically 

 similar but differ in physiological respects; of three 

 sense cells which are found in the chemosensory 

 sensillae on the labellum of dipterans (flies), only 

 two send peripheral fibers into the chemoreceptive 

 part of the hair (fig. 11). These two cells react to 



