NONPHOTIC RECEPTORS IN LOWER FORMS 



377 



FIG. 12. Schematic drawings of the structure of an insect 

 campaniform sensilla (left) and an arachnid iyriform organ, a 

 slit sensilla (right). The arrows show the probable direction of 

 the stimulus exciting the sensilla. These diagrams are based on 

 drawings of the base plate sensilla on the haltere of Calliphora 

 (Pfiugstaedt, 191 2) and of the Iyriform organ on the patella of 

 a spider, ch, chitin cuticle; hy, hypodermis; sc, sense cells; 

 sf, surface (Vogel, 1923). [From Pringle (97).] 



particular differentiation of the cuticle, the peripheral 

 branches of which terminate between the cells of the 

 hypodermis, e.g. in the skin over the joints in the ap- 

 pendages of Limulus (16, 98), or in the crustaceans 

 (126); 6) campaniform sense organs of the insects 

 (fig. 12) and slit sense organs of the Arachnoideae 

 (fig. 12) in which bipolar sense cells send their 

 peripheral fibers to special diff"erentiated structures of 

 the cuticle at the membrane of the joints (66, 95, 97, 

 128); f) hair sensillae (sensillae trichodeae), which 

 consist of single or larger groups of hairs, at the basis 

 of which enter the peripheral ends of bipolar sense 

 cells (fig. 1 3) — because of their location they are more 

 or less affected by the relatixe positions of adjacent 



segments of the appendages (95) or of the body, e.g. 

 of the head according to Mittelstaedt (86), as shown 

 in figure 14. 



In the interior of the body are located: a) muscle 

 receptors in insects, as shown by Finlayson & Lowen- 

 stein (40) and Slifer & Finlayson (121); ti) organs 

 suspended between two movable segments found in 

 Limulus (16, 98) and Crustacea (especially the stretch 

 receptor organs shown in fig. 15) (i, 2, 3, 4, 22, 23, 

 37, 38, 42, 74, 75, 140). To this latter group also 

 belong with high probability many chordotonal or- 

 gans which are found in the body of insects (fig. 18). 

 This topic has been reviewed b\' Eggers (35) and by 

 Snodgrass (123). 



Proprioceptors in the wings of insects (124) and in 

 the abdominal part of Dytiscus (62) have been found 

 by physiological experiments; they are however not 

 yet identified anatoinically. In earthworms Gray et al. 

 (49) found sensory discharges upon passive stretching 

 and Prosser (100), during active movement. 



The adequate stimulus for the multipolar sense cells 

 on the skin of the joints of Limulus, for the campani- 

 form organs of the insects and for the slit sense organ 

 of the arachnoids is tension or coinpression of the 

 cuticle covering the organ. The receptors in the 

 muscles of the insects and the stretch receptors of 

 Limulus and of the crustaceans respond to increase or 

 decrease of the tension. All these organs are — with 

 the exception of one of the two neurons in the stretch 

 receptors of the crayfish — tonic receptors with slow 

 and incomplete adaptation. The same holds true for 

 the hair sensillae on the joints of the insects. Phasic 

 receptors in close proximity to the tonic neurons are 

 often found. They respond to an adequate stiinulus 



FIG. 13. Schematic diagrams of hair sensillae, that on the left from the cercus of the cricket 

 Liogryllus campeslris with an intraepithelial sense cell, and that on the right from the caterpillar 

 Pieris with a subepidermal sense cell, ch, chitin cuticle; ha, chitinous hair; hy, hypodermis; nl, 

 neurilemma; sc, sense cell; to, tormogen cell (secreting the chitinous joint membrane). [From 

 Weber (137).] 



