268 W. J. CEOZIER AND LESLIE B. AREY 



reaction involves a deep insinking of the dorsum at the level of 

 the 'eye spots.' This form of 'reflex' is seen also in other Dorids 

 (C. roseapicta, Lamellidoris, etc.). 



The tentacles do not easily become exhausted. After ten to 

 fifteen successive applications of a glass rod, a tentacle is still 

 reactive to light touch, although the resulting contraction is not 

 so complete. 



The 'rhinophore' of Chromodoris (Arey, '17, '18) is a some- 

 what complex structure. Its extreme distal tip is usually pale 

 blue or white, the rest of the organ deep blue or purple. On 

 either side of an anterior, median line, which is plain and smooth, 

 the 'rhinophore' bears a series of twenty-eight projecting leaves. 

 To a light touch at the extreme tip, a 'rhinophore' responds by 

 partial retraction; the anterior, unmodified, median hne is less 

 sensitive; the posterior and lateral surfaces are the most sensitive. 

 Even moderate intensities of activation cause a 'rhinophore' to 

 be retracted within its collar, suddenly and completely, then 

 reextended, more slowly. In animals of average size (8 to 12 

 cm. long) the 'explosive' type of response is the result of even 

 light tactile stimulation. To a very delicate touch on the lat- 

 eral or posterior face the retraction is only partial. The ' rhino- 

 phore' is itself contractile, longitudinal contraction occurring 

 locally along its length when lightly touched, and it is pulled 

 within its collar by the operation of basilar muscles within the 

 'rhinophoral' pocket. The retraction of a 'rhinophore' involves 

 the subsequent sphincter-like closure of its basal collar. 



A 'rhinophore' is not easily exhausted. When approximately 

 the same spot on the side of the organ is touched fifty times at 

 ten-second intervals, the amplitude of contraction decreases, 

 but the 'rhinophore' is still reactive. 



Stimulation of a 'rhinophore,' even repeated stimulation, does 

 not influence the homolateral tentacle. The 'rhinophore' reac- 

 tion is itself characteristically homolateral, as was seen particu- 

 larly in the case of abnormal variates in which the 'rhinophores' 

 were found naturally fused in varying degrees (Crozier, '17 e). 

 A sharp tap administered to one 'rhinophore' results in the 

 partial, less complete contraction of its mate, and also of the 



