730 SUMMARY OF CURRENT RESEARCHES RELATING TO 



cliaracteristlcs of the striated fibres of the Artliropoda, differing only in 

 the greater coarseness of the fibrils and of the networks. The develop- 

 ment of the primitively simple transverse network from intranuclear 

 fi.laments of adjacent intrinsic nuclei of the non-striated fibres is ren- 

 dered j)robable by the correspondence of the transverse band of nuclei 

 with tlie transverse network, and the replacement of the former by the 

 latter. The author proposes to deal with the simple type of striated 

 muscular fibre in another memoir. 



Growth of Transversely Striated Muscle.* — Dr. W. Felix has made 

 some observations on the growth of transversely striated muscle, chiefly 

 based on the study of human embryos. 



He finds that the young muscular fibre is hollow, and that the time 

 when it becomes solid is different for the same muscles in embryos of the 

 same age and for different muscles in one and the same embryo. The 

 nuclei lie in the central cavity (axial nuclei), in the transversely 

 striated mantle-layer (mantle nuclei) and in the periphery of the fibre 

 (contour nuclei). The transversely striated mantle of young muscular 

 fibres is not complete, but often exhibits clefts of various lengths. The 

 diameter of the several fibres of one muscle often varies considerably ; 

 it increases a great deal till the third month, between the third and 

 fourth month there is a considerable fall, and then again a regular 

 increase. From the middle of the third month till the end of foetal life 

 we find in each muscle fibres with multiplying nuclei arranged in series. 

 These fibres fall into two groups. In the first the fibre possesses several 

 rows of nuclei in its mantle layer, and the brightly coloured nuclei of 

 the rows differ in form, size, and distance from one another. In the 

 median part of the row they are closely packed and pressed into all 

 possible forms ; this is the site of the greatest growth-energy (and in all 

 probability corresponds to the nerve-ending) ; away from this they are 

 round, and then elongated. The fibres break up into daughter-fibres, 

 each of which contains a row of nuclei. Around the fibre there is 

 formed a sheath rich in nuclei and vessels; this appears before the 

 formation of the rows, increases gradually in thickness, and becomes 

 concentrically striated. "With increasing growth the sheath disappears. 

 Longitudinal division of fibres occurs not only in lately born infants, 

 but also in later years of life. 



The muscular fibres of the second group contain only one row of 

 nuclei in the central cavity. The dark-coloured nuclei are arranged 

 transversely, and differ little in size, form, or distance from one another. 

 There is no spot of greatest growth-energy, and there are no relations 

 to the nerves. Longitudinal division of the fibres has not been observed. 

 These fibres are found in the muscles of embryos two or three months 

 old. The rows of nuclei are found almost regularly at the ends of the 

 fibres, and are the expression of an active increase in length. Parts of 

 the fibres of the second group break up, and their products resemble the 

 sarcoplasts of Margo and Paneth. 



"While the muscular system is being laid down new fibres of the 

 embryonic type are constantly being formed. As soon as all the fibres 

 are developed there is a pause in the increase of tlie number of fibres; 

 this occurs in the third month. When increase begins again it is only 



* Zeilschr. f. Wiss. Zool., xlviii. (1889) pp. 22-1-59 (2 pis.)- 



