154 T. H. MONTGOMERY, JR. 



Now in each of these cases we notice in the polar body, as in 

 the egg, a larger and a smaller bipartite chromosome. Thus 

 in the polar body the larger dyad A, A, and the smaller B, B ; 

 in the egg the larger dyad a, a, and the smaller, b, b. As far as 

 I can determine this relation appears to be constant : one large 

 and one small dyad in the polar body as well as in the egg ; and 

 not two smaller (or larger) dyads in the polar body and two 

 larger (or smaller) dyads in the egg. Now from what we have 

 found to be the case in other objects, I would judge A, A to be 

 an entire univalent chromosome that had been paired previously 

 with the entire univalent chromosome a, a ; and that a similar 

 relation holds between B, B and b, b. This "would then be a 

 reduction division, separating entire univalent chromosomes. In 

 favor of this is the fact that A, A is approximately similar in vol- 

 ume to a, a, and B, B to b, b ; and we have learned that chro- 

 mosomes of similar volumes conjugate in synapsis. Two dyads 

 are left in the egg, a, a and b, b, each of which could be re- 

 garded as a longitudinally split univalent chromosome. In the 

 formation of the second pole body (Fig. 26) the two parts of 

 each dyad separate from each other, and this would be an equa- 

 tional division. There are then left in the egg the two chromo- 

 somes a and b, which differ markedly in volume. And this is in 

 exact accord with the fact shown in Fig. 27, that from each pro- 

 nucleus comes one large and one small chromosome. 



This interpretation would bring Ascaris into close agreement 

 with the other objects discussed in this paper : it explains why 

 there are two large and two small chromosomes in the fertilized 

 egg ; why each pronucleus has one large and one small chromo- 

 some ; finally, why the two bivalent chromosomes of the first 

 maturation mitosis differ in volume. The idea that each such 

 bivalent chromosome has been formed by a double longitudinal 

 splitting, hence that both divisions are equational, gives no ex- 

 planation for any of these phenomena, nor yet explains how or 

 why bivalent chromosomes should be formed. The onus no 

 longer rests upon us to prove the occurrence of a reduction divi- 

 sion ; but upon those of the other school to prove that a bivalent 

 chromosome represents one chromosome that has undergone a 

 double longitudinal division, and to show that such an interpre- 



