995 
less than 1 yw thick) the protoplasts of two opposite muscle-plates 
exert an influence on each other, in this way that the differentiation 
of the contractile elements sets in at corresponding points at the 
surface (the inside of the sarcolemma) or near it, and so the myo- 
fibrillae of one muscle-plate have corresponding fibrils in the opposite 
cells, lying exactly in the same line. But what is the nature of this 
influence cannot be discussed here. 
Thus we see that the myofibrillae can be traced to the sarco- 
lemma, but not beyond it, and that every fibril of a given muscle- 
plate has a fibril corresponding to it and lying in the same line in 
the adjacent myotome. 
In the stage of development following on the one just described, 
the larva greatly increases in length, and with this the myotomes 
lengthen considerably. The myofibrillae inside the muscle plates still 
extend from one extremity of the cell to the other, and so follow 
the extension of the myotomes. *) Now this longitudinal growth of 
the myofibrillae does not take place along the whole fibre, but only 
at two points near the ends. There where the cross striation of the 
musele fibre has been fully developed, a further Jengthening of the 
fibril is not possible any more; we never see any signs of a division 
of the anisotropic or isotropic portions of the striated sarcous seg- 
ments, the pattern of striation is always the same in all the muscle 
fibres of the different myotomes, and the breadth of the sarcous seg- 
ments is always of the same order. But when we study the muscle 
fibre closely along its whole course, we see that in this larval stage 
the striation of the myofibrillae does not extend to the extremity of 
the muscle fibre, but ends abruptly (for all the myofibrillae of a 
given muscle fibre at the same point) at some distance from the 
end, Here the myofibrillae of the same bundle are more or less 
fused together, thickened and so a’ sort of intercalated knot is 
formed, which takes a strong black stain when stained with iron- 
haematoxylin; at this point of the myofibrillae we must locate the 
lengthening, the longitudinal growth of the entire fibril. From this 
point onwards to the place of attachment of the fibrillae to the 
sarcolemma, a distance of about 10—4 u, there is no trace of a 
striation visible; the individual myofibrillae are again separated, 
attach themselves at different points to the sarcolemma, and here 
the fibrillae take a somewhat lighter stain than in the striated part 
of the fibre, and a stain which more or less resembles the colour 
of the collagenous connective tissue fibrils of a later period of develop- 
1) In his paper mentioned above, Dr. SunseR gives many drawings, which show 
several details of the process of differentiation of the myofibrillae. 
66* 
