VI CHONDRIOSOMES 197 



In the division of the spermatocytes the chondriosomes are presumably 

 generally more or less equally divided, along with the cytoplasm, between 

 the daughter cells, but definitely unequal distribution of chondriosomes 

 among spermatids has been described in Myxine (A. and K. E. Schreiner, 

 1908) and Eiischistus (Montgomery, 191 1). An unequal distribution of 

 the chondriosomes among the daughter cells also takes place in the 

 developing embryo of Ascidians (Duesberg, 1915). Thus precise quantita- 

 tive and quaUtative distribution of the chondriosomes between the 

 daughter cells at cell division is not at any rate of general occurrence, 

 nor is there any reduction in their mass at oogenesis. These facts weigh 

 heavily against the theory that the chondriosomes are the seat of 

 morphogenetic factors. 



(3, 4) The chondriosome apparatus always ^ plays a part, though 

 a variable one, in the structure of the adult spermatozoon. In what 

 may be called the " typical" spermatozoon it occupies the middle piece of 

 the tail, forming a sheath for some distance round the axial fibre. In 

 the tailless forms of spermatozoon, such as are found in Nematodes, 

 Arthropods, and a few other animals, it assumes various forms and 

 positions. 



It is quite possible that chondriosome apparatus, or part of it, always 

 enters the eg^ in fertilization. In several cases, it is true, the tail of 

 the spermatozoon fails to enter the egg, but in many spermatozoa only 

 the extreme base of it would be necessary, or in others {Ciona ; Duesberg, 

 1915) none of it, the chondriosome apparatus being alongside the nucleus 

 in the head. If the chondriosomes are to be accepted as hereditary 

 substance, however, it is necessary to show that having entered, they 

 mingle with the egg chondriosomes, and are distributed with them to 

 the cells of the developing embryo. 



The first form in which the behaviour of the chondriosomes at 

 fertilization was worked out was Ascaris megalocephala (Meves, 1911), 

 and this appeared to give brilUant support to the theory that the 

 chondriosomes are hereditary material. The chondriosomes in the 

 spermatozoon are in the form of a number of comparatively large 

 granules, those in the egg being much smaller, and scattered throughout 

 the egg cytoplasm. After the spermatozoon has entered the egg, the 

 egg chondriosomes concentrate round it ; the male chondriosomes 

 leave the spermatozoon and break up into numerous small granules of 

 the same size as those of the egg. The two sets of chondriosomes now 

 become indistinguishably mingled. 



It soon appeared that the case of Ascaris, in the spermatozoon of 

 which the chondriosomes are unusually bulky, is not typical. Meves 



* Montgomery (1912), however, describes it as being thrown off by the developing 

 spermatozoon ot Peripatus. 



