SENSORY REACTIONS OF CHROMODORIS ZEBRA 305 



salt influences the ionization of protein salts located at these 

 surfaces. The very beautiful experiments of Loeb ('18 a, b) open 

 a way to precise interpretation of this matter. The relative 

 effectiveness of various ions of neutral salts follows an order 

 familiar in many cases of physiological action, frequently regarded 

 as evidence of action upon the colloidal, as distinct from simply 

 chemical, properties of tissue proteins. These effects cannot be 

 interpreted in terms of 'permeability,' since, according to Oster- 

 hout's ('16) exact experiments, the influence of neutral salts 

 upon permeability does not follow this plan. Neither for salts nor 

 for acids can stimulation be regarded as due to increased per- 

 meability of the cell surface. 



d. Those reactions of Chromodoris which concern its 'behavior' 

 in the larger sense have to do with feeding and with copulation. 

 The generally accepted idea that the 'rhinophores' are speciahzed 

 chemoreceptive organs concerned with olfaction has been already 

 disproved (Arey, '17, '18). C. zebra does, however, give evidence 

 of being activated by low concentrations of materials secreted 

 by its companions. These reactions are chemopositive, they 

 are of several kinds, and they are important for conjugation. 

 It is also probable that chemoreception enters into food taking, 

 for it is only when creeping upon algae that the radula is 

 brought into operation. 



When several sexually ripe nudibranchs are placed in a dish, 

 they very soon protrude the genital papilla, and move toward one 

 another. In fresh sea-water, as, e.g., in an aquarium with running 

 water, conjugation is quickly effected."^ 



These nudibranchs produce constantly, when undisturbed, 

 more concentratedly if irritated (Crozier, '16 b), a curiously pene- 

 trating 'spicy' odor. This odor is evident in sea-water with which 

 they have been in contact. If the water is unchanged it assumes a 

 blue color owing to the secretion of pigment. In stagnant water a 

 Chromodoris may, but usually does not, protrude the genital 



^ According to Pelseneer ('11), and as we also have observed, many smaller 

 nudibranchs deposit several egg masses following each insemination. In Chro- 

 modoris this is not true, a single egg mass being the consequence of each insemi- 

 nation (Crozier, 'IS'^). 



