Sound in the Northumberland Lakes. 283 
On placing one of them, PI. VII. fig. 5, under the microscope, 
the tubercle was found to be vesicular, of a conical form, with the 
apex obtuse, and to resemble in texture the general surface of 
the animal: the basal portion contained an opake, rosy, granular 
body, a, of a glandular appearance, which completely filled the 
base of the tubercle; the apex, b, was pellucid, and on being 
attentively examined a crowd of very minute moving bodies were 
observed within it. 
Whilst watching with great earnestness the motion of these 
mysterious bodies, all of a sudden the apex of the tubercle burst, 
and a great number of them, cloud-like, rushing into the sur- 
rounding fluid, dispersed in all directions. The rupture appeared 
to close again, and the apex was seen to be almost empty; but 
fresh bodies making their appearance the receptacle was soon as 
full as ever. I have seen the eruption of these corpuscles on 
several occasions, and have no doubt that it is a natural pheeno- 
menon ;—not resulting from any artificial means,—certainly 
not from pressure, as the animals were always quite free. On 
examining these moving bodies, fig. 12, which are exceedingly 
minute, with 4th of an inch object-glass, they were found to be of 
an elliptical form, and to resemble spermatozoa ; tails, however, 
were not detected, though with a higher power it is not impro- 
bable that they may be found; for I could not satisfy myself of 
their non-existence. 
The nature of these tubercles or sacs is a matter of much 
interest. They were discovered by Ehrenberg, and described 
by him as the male organ,—the moving bodies being considered 
spermatozoa. Though I have not seen the original memoir on 
the subject, I think there can be little doubt of the accuracy of 
this opinion. How else can we account for the constancy of the 
appearance of these sacs ?—for their development at the time the 
eges are being produced, as we shall afterwards see is the case ? 
—for their being situated always on the same part of the ani- 
mal ?—for the contained gland-like body, and moving corpuscles ? 
—for the eruption of these latter bodies, and for their resem- 
blance to spermatozoa ? 
Having thus detected what I believed to be the male genera- 
tive organ, | was anxious to watch the development of the egg, 
which appears to have been already described more than once ; 
but as it has rarely been observed by British naturalists, I will 
venture to give my own remarks on the subject. The lower 
portion of the body, as before stated, is enlarged at the time when 
the male organ makes its appearance. On examining the en- 
largement, Pl. VI. figs. 1 & 2 b, 0, carefully, it is found to be 
usually greater on one side than the other; here it is opake and 
of a pale rosy hue, notwithstanding that the animal is faded 
