520 H. p. KJERSCHOW AGERSBORG 



in Hermissenda, Dendronotus, and Melibe (Agers- 

 borg, 1922 a : pp. 423-44). Indeed, as recently brought to light 

 by Gross (1921), on Nereis virens Sars, the general 

 integuments of this organism are sensitive to chemical stimula- 

 tion with a localization or concentration of the chemical sense 

 in the palps and tentacles, a circumstance correlated with the 

 rich innervation of these appendages and the relation of their 

 nerves to the brain. However, I have not yet found any 

 specialized receptors either in the dorsal tentacles or in the 

 cirrhi of nudibranchs. Their function, therefore, as far as the 

 nudibranchs are concerned, may not be so definite as previously 

 indicated. For this reason, and because of the facts brought to 

 light by experimental evidence (Copeland, 1918 ; Arey, 1918 ; 

 Arey and Crozier, 1919 ; Agersborg, 1922«), I have used the 

 original name tentacles, as employed by Alder and Han- 

 cock (1845. 1864), Hancock and Embleton (1848), and Gould 

 (1852), rather than the suggestive ' rhinophore ' as adopted by 

 Bergh and freely used by subsequent writers. For, although 

 the tentacles of the hood are highly specialized as indicated by 

 Alder and Hancock, Hancock and Embleton, and by my 

 drawings (PI. 27, fig. 8, PI. 29, figs. 15 and 16), it is now very 

 doubtful whether their function is olfactory per se, or even 

 slightly so. 



The remainder of the hood is apparently smooth, but upon 

 close examination it is found to be covered with tubercles, 

 a feature so common to the ectoderm all over the body of 

 Melibe leonina ; these tubercles are macroscopic in 

 M . f i m b r i a t a Alder and Hancock (1 864) , Eliot (1 902) . The 

 ventral side of the cowl (PI. 27, fig. 1, PI. 29, fig. 17) is concave in 

 M, leonina; muscle-fibres, radiating from the muscles of 

 the neck, support the veil. In the middle of the concave area 

 between the bases of the tentacles (PI. 29, fig. 17, B) is a marked 

 depression [Mdp). The ventral side of the cowl (PI. 27, fig. 6, En) 

 is tuberculate like the external side, but it has no odoriferous 

 glands (PI. 27, fig. 4, Oo, PI. 30. fig. 25, Og) : to be discussed 

 below. The head is set off distinctlv from the body bv a neck 

 (PI. 27, figs. 2, 3). 



