164 IIOUGHTONj ON THE FRY OF ANODONTA CYGNEA. 



opinion that the Glochidium is a parasite. The object of 

 this paper is to show that the so-called Glochidium of Rathke 

 is an undoubted parasite, though not in the sense in which 

 he and M. Jacobson understood it. My attention was lately 

 turned to this subject by my friend Mr. Busk, who, on the 

 occasion of a recent visit last April, informed me that the 

 young fry of the Anodonta had, some years ago, been observed 

 by Mr. Pollock to ,be parasitic upon fish. Mr. Pollock, it 

 appears, never published anything, and did not care to 

 make further investigations into this interesting subject. 

 As good luck would have it, the season for the exclusion of 

 the fry from the maternal branchiae had not passed over, and 

 I set to work immediately, with the following results, which, 

 hoAvever, are not to be regarded as establishing anything like 

 what remains to be investigated on the subject of the 

 parasitic nature of the Glochidia. On the 8tli of May I 

 examined five or six specimens of Anodonta cygnea, and found 

 that, in some instances, the branchiae were destitute of the 

 fry, while in others they were half emptied, showing that now 

 was the time for observation. On the 9th of May I opened 

 one of the Anodontas, and detached with the point of a knife 

 a portion of the contents of the branchiae, and put it into 

 a vessel of water, in which was a small stickleback {Gaster- 

 osteus leiurus), with a number of young fish recently 

 hatched. On the 1 1th of this month I examined the fish, 

 and found several Glochidia attached to the ends of the 

 pectoral fins, their valves being closed upon the fin rays, as 

 shown in the accompanying figure (PI. VII, fig. 10). This fact 

 sufiiciently proves the correctness of Mr. Pollock's assertion, 

 who is, in all fairness, entitled to the merit of the discovery. 

 Having several Sticklebacks in vessels of water in my rooms, 

 I repeated the experiment of placing Glochidia in the same 

 water with them. Some young Eels, about three inches long, 

 soon had their under surfaces completely beaded with the 

 parasites; the tail of the tadpole is also a favourite ob- 

 ject of attachment; to the larvae of insects the Glochidia 

 seem to have no afilection; I endeavoured to inoculate 

 the larva of Dyticus marginalis for instance, by drawing 

 clusters of Glochidia upon their bodies, but to no pur- 

 pose. The fins are the parts of the fish upon which the 

 parasites are chiefly found; but they are also parasitic 

 on any other projecting part of the body, as upon the 

 lips, the skin of the nostrils, and the orbit of the eyes;*" 



* From an observation of Dr. W. C. M'Intosh, it would seem that tlie 

 young of Mytilus edalis may also be parasitic. (' Observ. and Expts. on 

 Carc'mas moenas,' p. 17.) 



