HOUGHTON^ ON THE FRY OF ANODONTA CYGNEA. 165 



nor arc the parasites only external in their nature^ they may 

 be found abundantly within the gills of fish ; the small stickle- 

 back I alluded to above, owed his death, I have no doubt, 

 to their presence in the gills. One day I observed my poor 

 fish to be gasping, and quite unable, it appeared, to close his 

 mouth ; he died, and, on a post-mortem examination, I found 

 about sixty Glochidia fastened with closed valves upon the 

 gills; there were also several specimens of the strange and 

 interesting Gyrodactyhis elegans disporting themselves be- 

 tween the opercula; but the Glochidia Avere doubtless the 

 causa mortis. So far, the parasitic nature of the Glochidia 

 after their exclusion was established beyond question; but 

 I was anxious to discover instances of fish with the attached 

 Anodonta-ivj in a thoroughly natural state out of the canal 

 and pond. Through the kindness of T. C. Eyton, Esq., of 

 Eyton, to whom I am much indebted for facilities of natural 

 history investigation, I was enabled to examine a great 

 number of fish caught in a net out of the canal at Eyton, but 

 most disappointingly discovered not a single fish with any- 

 thing like a Glochidium attached ; the fish I examined were 

 roach, pike, and perch. About a week later, however, I 

 obtained from the canal not far from my house a small 

 perch, upon whose anal fin was a veritable Glochidium. The 

 comparative absence of these parasites from fish taken from 

 the canal, and the pool in which the Anodontce abound is very 

 striking ; it yet remains to be seen how far this parasitic 

 condition of tlie fry is essential towards their growth and 

 final development. So far as my investigations have hitherto 

 gone, I am inclined to believe that the above named condi- 

 tion is necessary to ensure their ultimate growth ; for my 

 attempts to keep the fry alive beyond a few days in vessels 

 of water in which there were no fish quite failed ; the young 

 died, and became the prey of numerous Infusoria, as 

 Leeuwenhoek, De Quatrefages, and other observers have 

 remarked ; but further observation is necessary before we 

 can arrive at any safe conclusion on this point. 



None of the sticklebacks, which had several parasitic Glo- 

 chidia on their fins, &c., on the 11th of May, aflbrded a single 

 example of a parasite on June 9th. During a greater part 

 of the intervening time I examined my attached specimens 

 almost dail3^ As far as the external form of the shell of the 

 young mollusc is concerned, I was unable to detect any 

 diff'erence, even up to June 2nd ; the internal animal, how- 

 ever, was becoming more developed. If a Glochidium, at the 

 time of its exclusion, is gently broken in the compressorium, 

 little more is to be seen than a nndtitude of round particles, 



