DEVELOPMENT IN CROSS-FERTILIZED EGGS 411 



takable cases of undivided chromosomes passing to one pole 

 (1). It is more difficult to decide in the case of the figures given 

 by Tennent (16), since the matter is compHcated by the presence 

 of the large V-shaped chromosomes of Toxopneustes. 



The evidence from fish crosses does not support the idea that 

 the chromosomal behavior is highly specific. If only certain 

 paternal chromosomes were affected, as Baltzer claims does 

 occur in certain of his crosses (1), then we would expect to find 

 in every anaphase of the first cleavage the same picture. This 

 is not the case. The amount of lagging varies. It also occurs 

 in the cleavage following the first and always at the anaphase. 

 In Baltzer's crosses, as his figures show, mitotic disturbances 

 appear in all of the early cleavages including the fourth. I 

 have elsewhere (14) emphasized the difficulties in the way of 

 identifying many of the extruded chromosomes in echinoderm 

 crosses. If elimination or unequal distribution depends upon 

 the specific nature of individual chromosomes, we would expect 

 more variability in the character of the disturbance, more regu- 

 larity in the extent of its occurrence during any one mitotic 

 phase, as well as an expression of its specificity during other 

 periods of the mitotic cycle. The fact that it appears only 

 during the anaphase, that it is variable in extent, and that it 

 occurs in the second, third, and fourth cleavages as well as in 

 the first is in harmony with the suggestion that the behavior is 

 the result of a general physical reaction between the egg cyto- 

 plasm and the sperm chromatin. 



All of the figures referred to strengthen the impression that 

 the disturbance is due to a general physical reaction involving 

 the entire sperm chromatin and the egg cytoplasm and is not 

 the result of a differential action of the egg components toward 

 individual paternal chromosomes due to the specific differences 

 existing in the hereditary quaUty of the latter. According to 

 modern ideas of heredity, the chromosomes determine taxo- 

 nomic characters. In so far they are specific. Their relation in 

 cell division is the same for all. If some paternal chromosomes 

 undergo abnormal distribution or ehmination and others escape, 

 it is a result of chance rather than of specific hereditary quahties. 



