670 [June 18, 



must be prepared when quite fresh, otherwise the fine nucleated 

 fibres are completely disintegrated. The capillaries were injected as 

 in the other cases*. 



In this thin muscle, networks formed by bundles of dark-bordered 

 fibres, consisting of from two to five or six, may be very easily shown, 

 and with high powers (700 to 3000 diameters) the very fine nucleated 

 fibres resulting from the division and subdivision of these in a dicho- 

 tomous f manner, can be readily demonstrated. 



In this thin muscle I have often followed individual fine nucleated 

 nerve-fibres, now over, now under muscular fibres, sometimes cross- 

 ing transversely, sometimes obliquely, and sometimes running for a 

 certain distance parallel to the fine muscular fibre. The drawing 

 accompanying this paper renders further description unnecessary. 

 I shall enter into full detail in my communication next session ; but 

 as the summer is the period to obtain specimens of the Hyla, I am 

 anxious my fellow-labourers in Germany should at once be acquainted 

 with the advantages of the thin muscle alluded to ; and I cannot 

 too strongly recommend this beautiful little frog, which they have 

 the advantage of procuring more readily than Englishmen, for micro- 

 scopical investigation. All the tissues are beautifully distinct, and I 

 challenge those who are interested in these questions to discuss them 

 with me, selecting the tissues of this animal for special study. 



EXPLANATION OF THE PLATE. 



Distribution of finest nucleated nerve-fibres to the very narrow elementary mus- 

 cular fibres of the mylo-hyoid of the little green tree-frog (Hyla arborea), 

 magnified 1 700 diameters. Drawn on the block by the author. 



The elementary muscular fibres are marked g, h, i, Tc. Jc is a very young one, 

 slightly stretched ; i is a fully-formed muscular fibre ; h, another stretched in its 

 central part. The nuclei of these fibres exhibit some differences in size and form. 

 Nucleoli are distinct in all, and in the fibre marked g the nuclei, which were 

 coloured by carmine, exhibit three different intensities of colour, the dark central 

 spot, " nucleolus," being most intensely coloured, as indicated by the shading in 

 the drawing. 



* As the details of the mode of preparing these specimens would occupy many 

 pages, I must defer entering into this part of the question ; and it is useless to 

 give the outline, as success depends entirely on minutiae. 



f The dichotomous division is most common ; but sometimes three, four, or 

 even five branches result from the division of one fibre, as is well known to be 

 the case in the common frog. 



