No. 2.] COMPARATIVE CVTOLOGICAL STUDIES. 499 



2 . Number of Nucleoli. 



As Flemming ('82) has stated, the number of nucleoli is 

 small in most cells, not more than from one to five. But in 

 certain stages of some cells there may be several hundred (ova 

 of Reptilia, Amphibia, Selachii^ nemerteans, subcuticular gland 

 cells of Piscicola). Even in those cases just mentioned, where the 

 number of the nucleoli is very large, the immature cell contains 

 only one or a few nucleoli, so that the large number is attained 

 only when the nucleus has increased in size, cf. the observa- 

 tions of Auerbach ('74a). Among somatic cells a large number 

 of nucleoli is much more infrequent than among egg cells. At 

 a given stage of a given cell of any one species of metazoan 

 the number of nucleoli is pretty constant, and there is less 

 variability in the number among those cells where the typical 

 number of nucleoli is a small one than in those where a large 

 number is present. In cells where the usual number of nucleoli 

 is one or two, as in those of the nidamental gland of Moii- 

 tagiia, three may quite frequently be found, but no cells are 

 found in which not a single nucleolus occurs ; in other words, 

 there is in most cases some degree of variability in the number 

 of the nucleoli, and the amount of this variability stands in a 

 more or less direct ratio to the number of the nucleoli, but it is 

 numerically progressive as a rule, tending to produce more than 

 the normal number, and in no cases where cells normally con- 

 tain nucleoli do we find a regressive numerical variation leading 

 to the total disappearance of nucleoli. In certain few cells no 

 nucleoli are present, and this is the case in more cells than 

 Flemming ('82) was disposed to admit, since not only are spe- 

 cialized cells like mammalian blood corpuscles without them, but 

 they are also absent in certain connective-tissue elements of 

 nemerteans, and in certain other cells of a low degree of vitality. 



Auerbach ('90) formulated the law that the number of nucle- 

 oli is more or less constant for all the cells of a given species. 

 But this conclusion is certainly erroneous, since in Doto there 

 is one nucleolus found in the blood corpuscles and in the ovum, 

 from one to five in the ganglion cells, from one to three in the 

 cells of the nidamental gland, and in the giant cells as many as 



