262 W. M. Baldwin 



the intervening sarcoplasm, as well as the fibrillae, is continued 

 beyond the limits of the sarcolemma end outside of the muscle fibre. 

 Still no attempt is made to explain with what the sarcoplasm be- 

 comes contiuous or where it ends. Were the condition true, as 

 the author has figured, then we should be compelled to modify our 

 conception of the sarcolemma as a closed tube or envelope confiniDg 

 the semifluid sarcoplasm. 



I have studied my own tadpole preparations with this parti- 

 cular point in mind and have represented in fig. 11 a muscle termi- 

 nation wbich may be considered as typical of the developing fibres 

 at this age. The tadpole measured 1,5 cm. 



I agree for the present with other investigators in naming the 

 nucleus, which is seen imbedded in the granulär protoplasmic mass 

 surrounding the muscle fibrillae, a myogenetic nucleus, and also in 

 referring to the investing membrane as sarcolemma (B). I have 

 carried this membrane around the muscle fibre end, since such is the 

 appearance produced when focusing down upon the fibre. It does 

 not represent the end of the muscle fibrillae, however, as might at 

 first appear, even in spite of their undififerentiated appearance. This 

 fact can be ascertained by focusing to a deeper level in the fibre: 

 then we get the appearance such as I have represented. The muscle 

 fibrillae terminale in a number of cone-shaped processes, whose 

 walis are formed of a delicate membrane, coutinuous with the sarco- 

 lemma, which bridges the ends of those fibrillae. This appearance 

 is similar of that observed in the muscle fibre represented in fig. 6. These 

 are the processes and this the membrane which have been over- 

 looked. The specific remarks which I have made upon foregoing 

 pages regarding the features to be noted in eonnection with fig. 6 

 apply equally well here and require no repetitiou. 



The presence of this unbroken rounded contour of sarcolemma 

 traversing the end of the muscle fibre, to which I have referred 

 above, is readily explained, if we will imagine the muscle fibre as 

 a whole rotated through an are of 90°. Where the sarcolemma 

 surface faces the eye it is almost perfectly transparent, but where, 

 however, it lies in a vertical optical plane, its contour becomes 

 manifest. Hence, the rounded sarcolemma- end appearance would be 

 demonstrated again in the rotated condition of the fibre by that 

 portion located at A in the figure. At the same time we can rea- 

 dily understand how the muscle fibrillae lying at a deeper level 

 appear to have passed outside of the sarcolemma. And when through 



