178 ON THE DEVELOPMENT OF THE ANIMAL TISSUES. 



are smaller in reptiles, and their size continues to diminish in insects, 

 in mammalia, and lastly, in birds, where they are the smallest of all. 

 In all these instances, however, an extensive range of size is observable, 

 not only in different species, but in the same animal, and even in the 

 same muscle. He then shows that all the fibrillae into which a primitive 

 fasciculus may be split, are marked by alternate dark and light points, 

 and that fibrillse of this description exist throughout the whole thick- 

 ness of the fasciculus ; that the apposition of the segments of conti- 

 guous fibrillse, so marked, must form transverse striae, and that such 

 transverse striae do in fact exist throughout the whole interior of the 

 fasciculus. He next inquires into the form of the segments composing 

 the fibrillae, and shows that their longitudinal adhesion constitutes 

 fibrillte, and their lateral adhesion discs, or plates, transverse to the 

 length of the fasciculus ; each disc being, therefore, composed of a 

 single segment from every one of the fibrillae. He shows that these 

 discs always exist quite as unequivocally as the fibrillae, and gives several 

 examples and figures of a natural cleavage of the fasciculus into such 

 discs. It follows that the transverse striae are the edges, or focal sec- 

 tions of these discs. Several varieties in the striae are then detailed, 

 and the fact noticed that in all animals there is frequently more or less 

 diversity in the number of striae in a given space, not only on contigu- 

 ous fasciculi, but also on the same fasciculus at different parts. 



" The author then proceeds to describe a tubular membranaceous 

 sheath, of the most exquisite delicacy and transparency, investing each 

 fasciculus from end to end, and isolating it from all other parts ; this 

 sheath he terms Sarcolemma. Its existence and properties are shown 

 by several modes of demonstration : and among others, by a specimen 

 in which it is seen filled with parasitic worms (Trichinae), which have 

 removed all the fibrillae. The adhesion of this sarcolemma to the out- 

 ermost fibrillae is explained. 



" It is also shown that there exist in all voluntary muscles a number 

 of minute corpuscles of definite form, which appear to be identical with, 

 or at least analogous to the nuclei of the cells from which the develop- 

 ment of the fasciculi has originally proceeded. These are shown to be 

 analogous to similar bodies in the muscles of organic life, and in 

 other organic structures. 



" The author next describes his observations on the mode of union 

 between tendon and muscle ; that is, on the extremities of the primitive 

 fasciculi. He shows that in fish and insects the tendinous fibrillae be- 

 come sometimes directly continuous with the extremities of the fasciculi, 

 which are not taper, but have a perfect terminal disc. In other cases 



