I MI-: i'i;- 53 



granules -tin- ' which in (In 



of tin- Sea-urchin ordinarily app- chromatic granule Lf found. 



upon the employment of the hk'heM magnifying l>o\\> 



ially in the study of objects i liu r . -^ d) tir>iv -uitable for thi> 

 purjo-e. to he a small V shaped loop. Tin* number of tip 

 chromosomes appears to be very definite, and subjeet to law for each 

 gpeciea of animal. 



At the tips of the gpindle there maybe demonstrated, in addi- 

 tion, two special and exceedingly niinut<> hodie>. one of which 

 occupir.- the exact centre of each of the two previously im-nt' 



ins of rays : they are, in fact, to be regarded as the cau-e of the 



Fig. 28. Liagram of nuclear division, afu-i H \m.. 



redone sees th.- .-pi ml If, composed of ilflir.it f ii"ii-riir<nii:iu<- tii 



ral; up.- aiul tin- i-hriiii! :t.- mitlilK-. The splitting of tin- til i- 



of the latter h.xs ;ilr<-;uly t.ik.-n pl.-i.v. In tiv'uif H tli-- ,l;nu-litfi-l.ip.- : i the 



.11 h ivf iiiuv.l ,-ipirt in ... ,,ns. In ri-m-f ''tlif\ bflgia to 



in a regular in;uiiif r into two groups of loops. In figure D the groups of l>a lie 



near the two poles <.f tin- .-pnulle. 



latter. Inasmuch as during the elongation of the nucleus tlu-\ 



to be found at each of its two pole>. they may he especially de>i;_rnated 



as i>t,l,i,' r,,,-jinscles [or centrosomes\. During th whole process of the 

 division of nucleus and cell-body, it apj c.-ir-- as though a directing 

 influence belongs to the two polar corpu-de>. 



Important changes in the nuclear loops of the .-j. indie take place 

 during later stages of the process of division. Kach loop is split 

 lengthwise into two <A///</ i (fig. 28 A), as di>CM\ered by 



l'i r.MMiXij and as confirmed since then by numerous other in 

 gators (STRASBUIIGER, HEVSKK. VAN I:I:\IPI:N. \l\\\\.. and others). 

 The>e (laughter-loops so<.n move apart toward the oppo>ite end> of 

 the spindle (tigs. 28 Ji, C] see also the explanat ion of the figures), and 

 approach very closely to the polar corpuscle- at their tips (tiir. 2 



Thus by a complicated process a division of the stainahle i; 

 substance into similar halves is brought about. As the immediate 



