6 HABITS. 



Like many of the true Annelids they also progress by floating on the surface of the 

 water, either crawling up the side of the vessel, and thereafter pushing their snouts outwards 

 from the water-line ; or, if the water is shallow, raising their heads upwards from the bottom 

 and gradually extending their snake-like bodies along the surface. As in the case of the 

 Nudibranchiate Mollusca, a track of mucus is constantly left behind them in this position, and 

 in the same manner they can be suspended by it. So abundant, indeed, is this mucus, that in 

 jars containing numerous vigorous specimens of Linens gesserensis a perfect gelatinous mesh- 

 work is formed near the surface of the water, and even throughout the entire vessel. I had 

 carefully tested by personal observation the correctness of the explanation given by Messrs. Alder 

 and Hancock of the modus operandi by which the Nudibranchs crawl on the surface of the water, 

 and the same explanation is very evidently applicable to this class. The adhesion of the body to 

 the mucus gives the animal sufficient purchase for the use of its facile muscles, for it need 

 scarcely be mentioned that the water has no influence in lessening the attachment. Hence the 

 remark of M. de Quatrefages, that Nemertes glides through the water by means of excessively 

 fine vibratile cilia, which are protruded from every part of the surface of the body, cannot meet 

 with our support. When anxious to view the ventral aspect to advantage, no difficulty has been 

 experienced in making many thus float on the surface of the water in the shallow trough of a 

 large dissecting microscope, for by constantly irritating the animals in their endeavours to crawl 

 along the bottom of the vessel, and arresting their progress, they at last pushed their snouts 

 upwards, and sought refuge by this mode of progression. 



While possessing the power of crawling and floating just mentioned, some species also 

 swim freely through the water, and this habit in Britain is especially characteristic of the forms 

 which inhabit deep water; indeed, I am not at present aware that littoral species exhibit it 

 in any degree, though there is nothing inimical in their conformation. This habit has been 

 noticed in the Cerebratulus marginatus of Nardo, the Meckelia aurantiaca of Grube, and by M. 

 de Quatrefages, in his Folia bembioe, dredged off the coast of Sicily. Four British species, as far 

 as at present known, show this mode of progression, viz. Amp/iiporus specfabilis, A. pidcher, 

 Micrura fusca, and Cerebratulus angulatus. When irritated, each throws itself on its edge, 

 and by alternate lateral strokes of the tail propels itself rapidly through the water with a serpen- 

 tiform wriggle. Thus, their mode of swimming closely resembles that of the freshwater Nephelis, 

 and differs from the horizontal flapping of their allies, the Planariae, which M. Duges compares to 

 the motion of the Bays. The British species above noted are characterised by their somewhat 

 short and broad form, and especially by the production of the lateral margins into a thin edge 

 throughout the greater part of the body. 



Many of the Nemerteans, as M. de Quatrefages mentions, are very hardy in confinement, if 

 the observer is at all experienced in the management of such animals. It is not by the well- 

 calculated adaptation of plant to animal life, of nicely balanced conditions supposed to be 

 favourable to the healthy continuance of marine existence in these artificial states, that the 

 experiment is always successful. Pure sea-water in clean glass vessels, and, in some instances, 

 a clean shell or empty Balaam, with a little sand or gravel on the bottom, constitute the most 

 suitable aquaria. Unless the vessel is large, only one or two examples should be placed in each, 

 and this is a point of great importance ; indeed, in the case of rare or valuable specimens, solitary 

 confinement has generally been resorted to as most advantageous. I have thus been enabled to 

 keep alive at a great distance from the sea-coast numerous individuals of Linens marinus, L. 



