236 Robert Thompson Young, 



Here there is little question as to the origin of all the nuclei. 

 The diiference in staining- property of different nuclei is very clearly 

 shown, to which point reference will be made later. In nucleus x 

 the clear zone surrounding the central granule is very evident, 

 while the small granules on its periphery will probably take part 

 in forming a nuclear membrane. It is probable that from the two 

 groups of granules shown imbedded in the protoplasmic mass more 

 than one nucleus to each group will be formed, the granules sepa- 

 rating from each other to form smaller groups. Usuallj^ a single 

 nucleus does not contain as many granules as are represented in 

 each of these groups. Other masses of cytogenic protoplasm are 

 shown in Figs. 34 and 51. These, however, present no features 

 different from those already described. 



Perhaps none of the tissues of the larva present this spontaneous 

 cell generation as beautifully as does the nervous tissue in the 

 developing cephalic ganglia. This is because of the large size of 

 the developing ganglion cells- and their comparative isolation from 

 other tissues (see Figs. 62 and 63). 



The application of the term "nucleolus" to the nuclear granules 

 as has been the custom hitherto appears to me unfortunate. 

 Containing, as they do in many cases, most of the staining matter 

 of the nucleus, thej' represent rather the chromatin than the true 

 nucleoli. In this connection the representation by Child (1904, 

 Fig. 10) of a close skein arising from a "nucleolus" in Moniezia ex- 

 pansa is of interest. 



What is the source of these granules? It is evidently the un- 

 differentiated cytogenic protoplasmic masses. The reader may ask 

 at this point what proof there is to show that the granules arise 

 independently of other granules. May they not arise by division of 

 pre-existent granules? I have made a very careful study of this 

 point and while I am not prepared to deny absolutely such an origin 

 to the granules, I can say that the weight of evidence is 

 against such a theory. Obviously in a rapidly growing tissue 

 such as is found in an immature larva, where the nuclei are so 

 closely packed together that in many places they appear to be in 

 actual contact (Fig. 17 ^)) it is impossible to answer this question. 

 But in places where the tissue is more open, I have succeeded in 

 several cases in locating developing granules of Vg (.i in 



1) An actual contact of nuclei is not shown in the figure. 



