136 THE MICROSCOPE. 



and have nuclei either upon the surface (Cicada) or in the middle 

 (Libellula). In some insects the fibrillas are arranged as in a folded 

 lamella, the leaves of the folds running out from the center of the 

 fibre towards the surface, seen in cross-sections. The nerve-fibres 

 terminate in motor-plates (probably several for each fibre), consist- 

 ing of a granular basal substance, in which are embedded the rami- 

 fications of the axis-cylinder. The wing-muscles are more readily 

 dissociated into fibrillar than those of the rest of the body, from 

 which they are further differentiated by the absence of a true sarco- 

 lemma. — [Arch. ital. biol., ii. 131.) — C. S. M, in Science. 



Extreme Minuteness. — When vision is not aided by any 

 magnifying process, there is a point of minuteness, as all know, 

 when an object will make no impression upon the retina, and will 

 not be seen by the unaided eye. But when the object is viewed by 

 means of a microscope it becomes visible. There is a question, 

 however, that remains unanswered, which is, whether any object 

 may become so attenuated that it cannot be made visible by any 

 means. Not many years ago, less probably than twenty-five, there 

 were lines that could not be resolved by any microscopic lenses then 

 in existence, which can be exhibited now without any difficulty; but, 

 at that time, makers of lenses had not attained to the skill of mak- 

 ing them with large angles of aperture, but now they are made with 

 the highest angle that is possible, and, consequently, the capacity of 

 such objectives can only be increased by greater skill in their manu- 

 facture. But the limit of angle of aperture having been reached — 

 no opportunity remaining of increasing capacity in that direction — 

 is it not reasonable to suppose, that, with present appliances, no 

 greater skill in manufacture can be expected ? Sir Royston Pigott, 

 recently, at a meeting of the R. M. S., stated that he had seen 

 globules of mercury, made by smashing a minute particle of mercury 

 with a watch-spring, less than jfa of T fl 6 of an inch, or less than 

 the millionth of an inch. Another member replied that he was not 

 aware that there is any limit of visibility in the microscope other 

 than that imposed by the sensibility of the observer's retina, the cor- 

 rection of the objective and the illumination. 



The question is an interesting one and we may recur to it again. 



Preserving Insects, Crustacea, Worms, and Small 

 Vertebrates. — Professor K. Mobius finds that convenient prepara- 



