Muscle-Columns which form the Wing-Muscles of Insects. 285 



considerable length to the views and statements of other recent 

 writers on the same subject, and to indicate the bearings of these 

 observations upon the wing- muscles on the more intricate subject of 

 the structure of the leg-muscles of insects, and of the ordinary skeletal 

 muscles of vertebrates, I have omitted such references and indica- 

 tions from the present notice. I may simply state, however, that for 

 reasons which are given at length in the article above referred to, I 

 regard the structure of the wing-muscles of insects as furnishing the 

 key to the understanding of muscular structure in general, and I 

 believe that it is possible to draw a comparison detail for detail 

 between the two kinds of muscle which shows a complete correspond- 

 ence in all essential particulars. 



DESCRIPTION OF THE PHOTOGRAPHS. (PLATES 4 AND 5.) 



All the figures upon these plates are photographs of parts of sarco- 

 styles of the wing-muscles of the common wasp, which had been 

 prepared and stained by the method mentioned on page 281. In 

 specimens thus prepared there is a considerable amount of variation 

 in the degree to which the sarcostyles, and even the sarcous elements 

 of the same sarcostyle, are swollen by the dilute formic acid, into 

 which the muscle is placed after having been acted upon by gold 

 chloride. This is noticeable in fig. 8, a part of which is further 

 magnified in 8a, where, in the same sarcostyle, some of the sarcous 

 elements are narrow, and others wide. The latter do not, I believe, 

 belong to contracted or retracted portions of the sarcostyle, but are 

 merely more swollen by the acid, probably because they happened 

 to be less fixed, i.e., coagulated by the previous treatment with 

 alcohol and gold. It is noticeable also that these more swollen 

 sarcous elements are fainter in the photographs ; this is due 

 to the fact that they are always of a bluish tint; whereas the 

 less swollen sarcous elements are deep-red, and hence come out 

 nearly black. The former, however, show the longitudinal striation, 

 i.e., canalisation, better than the latter. It must further be stated 

 that the extension of the sarcostyles shown in fig. 8 has been produced 

 in teasing the preparation with needles by the demi-desiccation 

 process ; it is quite different from the extension shown in figs. 3 and 

 4, which has been brought about in the living tissue prior to the 

 advent of the hardening fluid. The sarcostyles represented in figs. 

 1 and 3, and the lower part of fig. 4, have been specially selected to 

 illustrate the characteristic appearances of retraction (? contraction) 

 and extension, because they were very distinctly red-stained and 

 showed neither distortion from being swollen by acid nor dislocation 

 from mechanical stretching after hardening ; all the other sarcostyles 

 rthich are shown in the photograph exhibit such distortion or disloca- 

 tion to a greater or less extent. 



