ON THE ZOOLOGICAL STATION AT NAPLES. 541 



interesting modifications in the Opistliobranchiata. This I did by obser- 

 vations on the living animal. Thus, for instance, the mantle of Ai^lysico 

 was found sometimes to exhibit a motion the effect of which was to keep 

 the water in circulation ronnd the gills. Again, a remarkable process of 

 flaccid skin at the front end of the mantle was found to play an important 

 part in conjugation. I found it also very instructive to ascertain the 

 strength and direction of the current of water in the pallial cavity and 

 elsewhere. Thus in Aplysia depilans and A. punctata the current was much 

 feebler than might have been expected, and in Aplysia limacina it was 

 even more so, while in other forms there was none at all. These and 

 similar facts were noted throughout a variety of forms, and enabled me 

 to deduce some general conclusions — for instance, that the development 

 of the osphradium is in intimate relation with the presence and strength 

 of the current of water, e.g., that in Aplysia depilans, where there is a 

 distinct current, the osphradium is more highly developed than in Aplysia 

 limacina, where the current is markedly less, and that where, as in 

 Pleurobranchoia or Umbrella, there is no current of water passing over 

 the gills, but is drawn directly into them, there is no sign of an osphra- 

 dium. Again, where, as in Pleurohranchus, the current first passes over 

 the rhinophora, there is no osphradium. This is more markedly the case 

 in the Nudibranchiata, where the place most exposed to the influence of 

 water was found to be the rhinophora. By facts of this nature, and also 

 by a comparison with the Proso branch lata, as far as my time would allow, 

 I was confirmed in my belief that there exists a relation of direct pro- 

 portion between the current of water and the development of the osphra- 

 dium, there exists a relation of indirect proportion between Osphradium 

 and Rhinophora, and that the Osphradium, whose function has hitherto 

 been regarded as obscure, is to be explained as an ordinary olfactory 

 organ in the same sense as the rhinophora are olfactory organs. To 

 further confirm this I made a series of experiments, but although these 

 seemed to be confirmatory they were not decisive. This difiicult 

 physiological work has still to be much further developed. 



By direct observation of the living animal I was able to note the 

 details of the contraction of the gills by which the blood is propelled ; 

 also to find some renal openings difiicult to discover in preserved material. 

 I found also in the remarkable gland before the gills in Pleurohranchcea 

 that there existed a current of water passing over the orifice and down 

 under the gills ; also that there was no excretion of mucus on irritation. 

 I was thereby enabled to draw some conclusions as to its function. I 

 found these and similar facts as instructive as the anatomical details I 

 had previously ascertained. 



With Golgi's methods I had no more success than others who have 

 tried them on the same animals. 



With the methylen-blue method of staining living nerve fibres I at 

 first had also little success, but ultimately succeeded in getting a good 

 colouring by laying the nervous system bare and leaving it for about 

 twelve hours in a weak solution (ooVo P^^' cent.). Among other things I 

 was enabled by this means to convince myself that no direct connection 

 by means of nerve fibres exists between osphradium and cerebral ganglia, 

 as has been found to be the case in lamellibranchs, though sections cut 

 and coloured in the usual way present an appearance which might be 

 mistaken for this. 



I had considerable trouble in finding a suitable fluid for dissociation, 



