GERM-CELL HISTORY IN THE BROOK LAMPREY 65 



other hand, it is assumed that if the female produces two kinds 

 of eggs which differ in their chromosomal structure by the pres- 

 ence or absence of a sex chromosome or chromosome complex, 

 the male must produce only one kind of spermatozoa. In this 

 case one-half of the ova should correspond to the spermatozoa 

 in their number of chromosomes. Guyer ('16) says that in the 

 fowl, where it has been shown experimentally that the female is 

 heterozygous for sex, there are also two kinds of spermatozoa. 

 He believes it is probable that only the spermatozoa containing 

 the odd element become functional. 



In the lamprey no evidence has been found of the presence of an 

 accessory chromosome in the oocyte during the synaptic phase, 

 the growth period, or the maturation division stage. A search has 

 also been made for this body in the spermatocytes during the 

 various stages of maturation, but without success. If, as seems 

 to be the case in some invertebrates and in Necturus among 

 vertebrates (King, '12), the sex chromosomes might be united 

 with other chromosomes, it would be extremely difficult to find 

 it in forms like the lamprey where the chromosomes are very 

 small and numerous. Observations on the lamprey can neither 

 affirm nor deny the existence of sex chromosomes which might be 

 responsible for sex. It can only be said that such a body has not 

 been found. Whether or not the assumption of the presence of 

 such a body is necessary to account for sex in forms like the lam- 

 prey where the sex potentialities are so equally balanced, is a 

 question which will be discussed later. 



I have not found in the lamprey a transfer of visible material 

 between the nucleus and the cytoplasm of the oocytes during 

 the synaptic period, but have found that there is an intimate 

 relation between the two parts of the cells. The absolute amount 

 of cytoplasm decreases greatly during this stage, and it is not 

 until the nucleus enters the diplotene phase that the cytoplasm 

 begins to grow again. All the energy of the cell seems to be 

 devoted to nuclear changes in the early oocyte and to cytoplasmic 

 changes during the growth period which follows synapsis. The 

 mitochondria, which are abundant in the oogonia, disappear dur- 

 ing the synaptic phases or, at least, can no longer be seen. In 



