1902.] NICHOLS — SPERMATOGENESIS ONISCUS ASELLUS LINN. 87 



A well-marked mid-body is visible in the late anaphase (Fig. 

 6ia). The interzonal fibres are sharply constricted and oftentimes 

 the nuclei completely separated before a cell wall makes its appear- 

 ance. In stages like this a noticeable bending of the fibres is often 

 observed. This is slightly evident in Fig. 61 a. 



Apparently the plane of the second spermatocytic division is to 

 be at right angles to the first, if Figs. 6 id; and 61^ are interpreted 

 as early stages in the formation of the equatorial plate of the second 

 spermatocyte. 



The equatorial plate of the second spermatocytic division is 

 shown in lateral view in Fig. 62. The length of the chromosomes 

 is less than that of the chromosomes of the first spermatocytic 

 division. The question as to whether the second division is actu- 

 ally equational is difficult to decide. The chromosomes of the 

 first maturation figure, consisting of a double row of four granules, 

 are separated by karyokinesis into halves, and each half contains a 

 double row of two granules (Fig. 58). It thus has the appearance, 

 although only the appearance, of a true tetrad. It will be seen 

 that some of these daughter chromosomes have a length equal to 

 their width, whereas in others the length is slightly greater than 

 the width. If we turn to the fully-formed spindle of the second 

 division (Figs. 62, 6$) we find similar phenomena. It might be 

 argued from these appearances that the second division is also 

 reducing. In view, however, of the weight of evidence in favor of 

 both methods of division (equation and reduction) being necessary 

 to the maturation of the sexual cells among the Arthropods, I hesi- 

 tate to accept this interpretation without further corroborative 

 evidence. When the length of the chromosomes is equal to their 

 breadth, it is obviously as impossible to decide here concerning the 

 plane of division as in the case of the true tetrads of the Copepods, 

 Canthocamptus^ Heterocope or Diaptomus. If the length is greater, 

 as in the anaphase, the appearance might be referred to the elonga- 

 tion of the mother chromosome (Figs. 49, 51, 53), some of the 

 daughter chromosomes not having recovered from the stretching 

 apart of the chromatin in the metaphase. The apparently greater 

 length of some of the chromosomes in the spindle of the second 

 division (Fig. d^) may be explained by the assumption that some 

 of the chromosomes commence to divide earlier than others, and 

 consequently become elongated, an assumption which is not with- 

 out parallel in the first spermatocytic and especially in the sperma- 



