572 Occurrence of Dreisse?ia poly morpha Vanb. 



it was difficult to see whether she was carrying her young 

 one or not. As the young increased in size (which they 

 soon do) and in weight, the undertaking became more diffi- 

 cult. We then saw the mother turn the young one on its 

 back, and, while she held the thigh in her mouth, the fore 

 legs of the young one were clasped round her neck. Some- 

 times, when she was attempting to jump upon some earthen 

 pots which I had placed in the cage, she was overbalanced, 

 and fell with her young one ; but, as soon as she was near 

 the ground, she would drop the young squirrel, so as to 

 prevent her own weight from crushing it, which would 

 have been the case if they had fallen together. I have seen 

 the young ones carried in this manner till they were half- 

 grown. 



The eye of the flying squirrel is of a most beautiful black, 

 large, and very prominent. The crystalline lens is nearly a 

 perfect sphere, and occupies at least two thirds of the whole 

 ball. It is of a very firm consistence ; and pressure, even less 

 than sufficient to cut it through with a sharp knife, renders it 

 quite opaque: greater pressure causes it to assume exactly 

 the appearance of spermaceti. I have found that pressure on 

 the lenses of others of the Rodentia, and of some fish (perhaps 

 of many other animals), will produce the same appearance, 

 though in different degrees. 



The processes attached to the fore legs, to assist in ex- 

 panding the wings, are cartilaginous in the full-grown young 

 squirrel ; whether it becomes bone in the aged, I have not 

 had an opportunity of ascertaining. The flying squirrel is 

 apt (like the monkey in confinement) to lose portions of the 

 tail. I fed my squirrels on milk, sugar, nuts, and any kind 

 of grain. I am sorry to add that this summer I have lost all 

 but one by some epidemic. 



Birmingham, Oct, 3. 1836. 



_— 



Art. IV. Notice of the Occurrence of Dreissena polymorpha 

 Vanbeneden in Northamptonshire. By the Rev. M. J. Berke- 

 ley, M.A. F.L.S. 



The Mytilus polymorph us Pallas was first recorded by 

 Mr. J. D. C. Sowerby, in 1824, as naturalised in the Com- 

 mercial Docks on the Thames, where it was probably brought 

 on timber. In 1834 Mr. Stark communicated to the Wer- 

 nerian Society the discovery of this species in the Union 

 Canal, near Edinburgh. During the present month (July) it 

 was found in considerable abundance, by the Rev. J. Streat- 



