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, Stickle- 

 back, 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 them- 

 selves 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. 



An 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. 



EXPLAJSTATION 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 ; e, retractor pedis muscle ; /, exhalant 

 eiphonal notch ; gg, probe passed throvigh from lower to upper 

 division of subpallial chamber, passing out at /'; h, oviduct. The 

 arrows indicate the direction iu which the ova pass. 



2. Ventral view of shell of young Anodoji, 101 days after first attachment 



to host and about 25-30 days after the end of parasitic life. The 

 Glochidmrn-^oil 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 half- 

 way along its length. 



3. Lateral view of iomewhat older Anodon. 



