120 



INTRODUCTION TO CYTOLOGY 



regular distribution of the chondriosomal substance in Gryllotalpa 

 strongly favors the view that this substance is of some significance in 

 heredity. It is probable, however, that the majority of cytologists regard 

 the evidence brought forward in support of the view as very inadequate. 

 Wildman (1913) points out that the chondriosomes may be largely lost 

 during spermatogenesis, and others have recalled cases in which the 

 nucleus is the only portion of the male gamete which can be seen to enter 

 the egg at fertilization. Meves (1911, 1915) and Benda, on the other 

 hand, show that chondriosomes also enter, at least in the forms studied 

 by them (Fig. 45). In the animal spermatid the chondriosomes appear 

 most commonly to contribute to the formation of the Nebenkern of the 



spermatozoon (La Vallette St. George 1886; 

 Popoff 1907; Chambers 1915; Shaffer 1920; and 

 others), in some cases later elongating into a 

 sheath around the axial filament of the tail 

 (Shaffer on Cicada). Duesberg (1919) states 

 that although the fate of the chondriosomes of 

 the spermatid varies in different animals, they 

 are nevertheless always present in the sperma- 

 tozoon, and that it has not been clearly shown 

 in any case that they do not enter the egg at 

 fertilization. In many eggs which they do enter, 

 however, they behave with great irregularity 

 during the subsequent cleavage stages (Van der 

 Stricht, etc.). It is not at all improbable that 



Pig. 45. — r ertihzation in . ' r 



FiiaHa papulosa, showing they are in some way concerned in the reactions 

 chondriosomes of sperma- through which hereditary characters are de- 



tozoon (at top) distributing , . . 



themselves in the cytoplasm veloped in the individual, but the general 

 ?oiK h f egg * ( A f ter Meves > opinion is that their apparent variability and 



indefiniteness in behavior in so many cases are 

 against the view that they take any part in the transmission of factors 

 upon whose presence the development of the characters depends 

 (Gatenby 1918, 1919). The equal distribution of chondriosomes at 

 the time of cell-division is thought to be without any significance in 

 this connection by Harper (1919). 



It is obvious that much work remains to be done before the possible 

 relation of chondriosomes to heredity and development can be made 

 clear. For the present it is safest to assume, as will be emphasized in 

 later chapters, that hereditary transmission is the function of the nucleus, 

 chiefly if not entirely, since the chromosomes afford a mechanism of 

 precisely the kind required to account for the observed distribution of 

 hereditary characters. 



Meves (1907a6, 1909) and Duesberg (1909) have also called attention 

 to the close relation of chondriosomes to muscle fibers in the developing 



