VOL. XXVII.] PHILOSOPHICAL TRANSACTIONS. 703 



Microscopical Observations on Muscles, and the manner of their Production. In 

 a Letter from Mr. Leuwenhoeck, F.R.S. N^ 336, p. 529. 



"^1 have long observed that the shell fish, called muscles, lay their eggs on the 

 outside of their shells ; and that so regularly one by an other, that they may 

 be compared to a string or band. These eggs, or imperfect muscles, lying on 

 the shells, continually increase in strength, till at last they come to be perfect 

 muscles ; but then you may see remaining on the shells a part of the egg-shell, 

 which sticks fast to the said shell, till the skin or membrane, with which the 

 muscles are encompassed, is changed. 



In August 1710, I procured some muscles, and dissected them according to 

 the best of my power; and found within the shells on both sides of the muscle, 

 against the parts of the fish, very thin and weak membranes; which I have 

 taken often out of the muscles, and placing them before a microscope, I have 

 seen a vast number of motions in the said membranes. And I observed those 

 appearances, not only in one, but all the muscles I dissected, especially in such 

 as had not been long out of the water. 



I placed a small particle of the membrane before a microscope : and though 

 that particle was not a hundredth part so large as a common grain of sand, yet 

 I discovered an incredible number of motions in it : and those motions were 

 not only circular, but I could discover at least 50 slender particles in the length; 

 which appeared through the microscope equal to 6 hairs breadth, and the thick- 

 ness of one hair, as they appear to the naked eye. And these motions con- 

 tinued so long, till cur eyes were weary of viewing them ; but as soon as the 

 moisture of the muscle, in which the said particle lay, was evaporated, the mo- 

 tions were ended. The minute particles that lay round about, were put into 

 such a motion, that one would have taken them for little living creatures. 



I have endeavoured for several years to discover the ovarium, or egg-nest, in 

 the muscles; and now lately, Nov. the 18th, there was a present made me of 

 exceedingly fine and well tasted muscles; some of which had placed their eggs in 

 part on their shells. This occasioned me to dissect several muscles again; when 

 at last I discovered the ovarium of the muscle, and in a great many of them 

 could see the unborn muscles as perfect as we could see them with our naked 

 eyes ; lying with their sharp end fastened to the string, or vessels, by which 

 they receive their nourishment. 



A few days after some muscles were brought me, which were very lean, like 

 some of the first muscles ; and among them I observed about 25 that had not 

 yet placed their eggs on their shells, but most of them were still shut up in the 

 ovarium, from which I took a great number of eggs ; which even through the 



