May, 1906.] .4 Reducing Division in Ascaris, 521 



of the chromosomes (already longitudinally divided) two by two 

 forming combinations of four members. 



From the resting nucleus a continuous spirem is formed in 

 the usual manner (figs. 1-3). In Ascaris the spriem is very 

 closelv wrapped so that it is a very difficult object to resolve and 

 cannot be untangled and traced out with confidence. This 

 however is a matter of no great moment in the present discussion 

 since the occurrence of such a spirem is well known. In some 

 cases (fig. 1-2) even before the spirem is formed the chromatin 

 is distinctly separable into two masses. Such a separation may 

 (fig. 5) or may not (fig. 3-4) be evident in the spirem. 



Before the contraction of the spirem has proceeded far the 

 granules which are strung along the linin thread become doubled 

 (fig. 4). At first very difficult to observe, the distance between 

 the doubled granules becomes greater and greater till the linin 

 thread sphts and two parallel sprimes are formed (fig. 5). It 

 has been maintained recently by Berghs (1) that in the flowering 

 plants these doubled granules arise not by a longitudinal splitting 

 of the spirem as has hitherto been supposed but by the conjuga- 

 tion of the granules from two separate strands of linin. Whether 

 the doubled spirem in Ascaris arises in such a manner or by a 

 split does not seem to me susceptible of complete demonstration. 

 I see, however, no reason for abandoning the older interpreta- 

 tion ; while there are several indications that point toward a 

 splitting rather than to a conjugation. (1) The spirem at the 

 earliest stage where the doubling appears (i. e. earliest as judged 

 bv the relative state of contraction of the spirem) is of approxi- 

 mately the same length (fig. 4) as the single spirem preceding 

 (fig. 3), while if a conjugation took place it would be of only half 

 the length. (2) At the earliest stage where the doubling is visi- 

 ble, judged by the same criterion, the granules lie exceedingly 

 close together and from this stage they recede up to a stage rep- 

 resented by fig. 5. while if they were the result of conjugation 

 we should expect the opposite. 



Very frequently in split spirems (fig. 5) the linin at one end is 

 bent into the form of a square with a prominent granule at each 

 comer. The granules are so much more prominent than the 

 linin thread upon which they are strung that one might easily 

 suppose that he was looking at the end of a set of granules doubly 

 split instead of at the side of a continuous spirem. In the cases 

 observed however there was no great difficulty in tracing the 

 course of the spirem and showing that such was only a superficial 

 appearance. The spirem in this stage often foreshadows quite 

 plainly the tetrads destined to be formed from it. In its contrac- 

 tion it is often thrown into two loops each arm of which is double 

 giving therefore two groups of four strands each. 



