INVERTEBRA.TA, CRYPTOGAMIA, MICROSCOPY, ETC. 281 



the fibres behave like uniaxial crystals. Treated with acetic acid or 

 boiled in water they undergo no appreciable change ; but jiotash and 

 nitric acid produce well-marked efiects. Thus, on adding a 5 or 

 10 per cent, solution of potash to a fragment of the teased-out tissue, 

 the fibres at once became swollen, those which were previously curved 

 straightened themselves out, and simultaneously the axial thread 

 almost completely disappeared. On then adding a 10 per cent, solu- 

 tion of nitric acid the fibres at once contracted, and the axial thread 

 became more visible than it had been before. Again adding potash, 

 the fibre expanded ; again nitric acid, and it contracted ; and as often 

 as one or the other reagent was applied, so often the same results were 

 produced. With strong acids the outlines of the fibres appeared to 

 vanish, and a homogeneous substance remained behind, in which the 

 axial thread remained wonderfully clear and distinct. On adding 

 magenta the threads stained deeply, but the matrix was not affected. 

 The fibres can best be separated from their tissue by macerating thin 

 slices for a few days in baryta water or 1 per cent, chromic acid 

 solution, and then teasing out. The muscular layer passes at its 

 distal margin insensibly into gelatinous connective tissue with fusi- 

 form corpuscles. The change seems to bo accomplished by the loss 

 of a distinct border to the muscle-fibres and the growth of the fusiform 

 axial thread at the expense of their hyaline portion ; at the same time 

 a distinct but small nucleus and nucleolus become clearly visible in 

 the axial thread, which has also acquired a granular character. 



The muscles of the sphincter are darker than those of tlie rest of 

 the muscular layer, owing to the increased size and proximity of their 

 axial threads, and to the development of fine granules in their hyaline 

 exterior. 



With carmine or magenta the axial threads of the muscle-fibres are 

 easily stained, but tlie hyaline part not at all ; hence when a section 

 of the muscular layer is stained the sphincters are made very promi- 

 nent, since their abundant nuclei lead them to acquire a very dark 

 colour. 



Mr. SoUas applies the term " muscle-fibres " to these structures 

 because they are morphologically similar to the fibres occurring in 

 otlier animals, to which no one hesitates to apply the term "mus- 

 cular," and the fact that, slightly modified, they enter into tlie composi- 

 tion of tlie sphincters of the cortical funnels seems to show that they 

 are functionally muscles as well. The specialization which converts 

 an indifferent cell into a muscular fibre consists simply of a limitation 

 of its contractility to a particular direction, so that it contracts in a 

 longitudinal and broadens out in a transverse direction ; its irritability 

 is by no means sujipresscd, and, as is well known, both striated and 

 unstriatcd muscles are capable of responding to thermal, chemical, 

 and meclianical stimuli indcjxMidently of any nervous stimulus. This 

 being so, all muscles, both those connected and those not connected 

 with a nervous ajiparatus, may be regarded as " neuro-rauscles," and 

 nothing is to be gained by introducing the term into our ncmienclaturo, 

 as Professor Haeckel suggests. It seems to imjily that in the muscles 

 of the higher animals some property has b(!en lost which was present in 



