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Show 58 MR. O. H. LATTER ON ANODON AND UNIO. [Jan. 20, VII. Glochidia distasteful to Fish. All fish with which I have experimented, viz. Perch, Loach, Stickleback, Minnow, have a strong dislike for Glochidia as an article of food. They frequently seize a mass of Glochidia floating in the disturbed water, but the mass is no sooner within the mouth than it is forcibly and emphatically rejected, being spit out to a considerable distance and very rarely (only once) attempted again. I do not think that it is the irritation caused by Glochidia attaching themselves to the inside of the mouth which makes the fish behave thus, for I killed six fishes which had tasted Glochidia within ten minutes of making the experiment, and in only one of them did I find a Glochidium attached to the mouth. There must, I think, be some unpleasant odour or taste about the Glochidia ; or possibly the " byssus," the shell-teeth, or both these latter combined, may serve to make the Glochidia uninviting morsels. VIII. Powers of Resistance of Adult Anodon and Glochidia. A n adult Anodon will live for at least a week, in cold weather, after it has been removed from the shell. I consider the animal alive so long as the cilia are beating and the heart is pulsating or capable of responding to a moderate stimulus. The Glochidia will live for a day or two within the gill of an apparently dead parent. I was very much interested to notice one morning after a severe frost that the water in the dissecting-dish where an Anodon lay removed from its shell was completely frozen. I allowed the frozen mass to thaw gradually, and then examined the animal and its Glochidia ; both were quite alive and none the worse for their severe exposure. I allowed the same animal and its young to be again frozen the following night, and obtained the same result. This power of being frozen and recovering must be of great importance in preserving the species in many of our shallower ponds and streams which are frequently frozen to the bottom in severe weather. EXPLANATION OF PLATE VII. Fig. 1. Diagram of Anodon to show course of ova. The left mantle-flap has been reflected towards the dorsal surface and also the left gill-plates. The free dorsal margin of the inner lamina of the internal gill-plate has been turned up to show the surface of the nephridium (organ of Bojanus). a, external nephridial aperture; b, genital aperture; c, reflected free portion of dorsal margin of inner lamina; d, ciliated external surface of nephridium ; c, retractor pedis muscle; /, exhalant eiphonal notch; gg, probe passed through from lower to upper division of subpallial chamber, passing out at /; h, oviduct. The arrows indicate the direction in which the ova pass. 2. Ventral view of shell of young Anodon, 101 days after first attachment to host and about 25-30 days after the end of parasitic life. The Glochidium-Bhell is shown outside the permanent shell, and the shell-teeth project inwards towards the middle line in such a way as to press upon and constrict the permanent shell at a point about halfway along its length. 3. Lateral view of somewhat older Anodon. |