300 Changes in the Muscle Cell of ISTecturus 



malian embryo. In view of the above facts I am led to the conclusion 

 that the fibrillse in the myoblasts of tectums bear no fixed or definite 

 relation to the cytoreticulum. 



C. Changes in Nuclei of Muscle Cell with Eeference to Changes 



IN Cytoplasm. 



relative volumes of nuclear and cytoplasmic material, move- 

 ments OF nuclei with reference to areas of cytoplasmic 



ACTIVITY, changes IN STRUCTURE OF NUCLEI. 



It is necessary to know the average sizes of the nuclei in the successive 

 stages of development before a comparison of the volumetric relations of 

 nuclear and cytoplasmic material can be made. The measurements given 

 in the following table were made from nuclei in teased fibres. Although 

 but ten measurements are recorded, these are typical of a much more 

 extended series. 



7 mm. 10 mm. 17 mm. 26 mm. 33 cm. 



1. 30 12 35 10 43 10 56 10 53 7 



2. 30 10 35 11 45 8 36 15 65 9 



3. 28 10 32 13 49 10 45 12 70 9 



4. 35 10 28 9 42 9 42 11 49 10 



33.1 10.4 32.9 11.8 45.1 8.6 47.3 10.8 56.3 8.2 



The numerals at the left represent the serial number of the nucleus meas- 

 ured. The numbers in millimeters above the columns give the lengths of 

 the embryos compared. The first column shows the length of the nucleus 

 in microns; the second the width. The numerals below these columns ex- 

 press the average length and width of the nuclei in the respective embryos. 



Since the nuclei are irregular in outline any estimate of their volumes 

 must be subject to considerable error. It will be seen by glancing at 

 the above table that the nuclei in the successive stages increase in length, 

 but that this is counterbalanced to a certain extent by a decrease in diam- 

 eter. It has therefore l)een thought best to consider the nuclei as 

 uniform in size and as representing a unit of volume. In computing 

 the volume of the cytoplasm the cells have been isolated and their lengths 

 and diameters measured. Although they are not of uniform diameter 



