No. 3.] THE PROTOZOA AND METAZOA. 757 



IV. SUMMARY OF OBSERVATIONS. 



1. The resting nuclei of Noctihua miliaris are large, round, 

 or oval structures, containing (a) chromatin in the form of karyo- 

 somes, and (b) "achromatin" in the form of large granules. 

 It is enclosed by a nuclear membrane which persists in part 

 throughout nuclear division. 



2. A cytoplasmic substance, corresponding to the centro- 

 sphere of many metazoan cells, is invariably present. It is a 

 permanent organ of the cell, often as large, or larger, than the 

 nucleus ; it divides to form an amphiaster, consisting of two 

 asters with connecting mantle-fibers, the central-spindle. 



3. During the division of the sphere the nucleus elongates 

 and bends to form a figure like the letter C ; the central-spin- 

 dle sinks into the opening thus formed, and is finally almost 

 enclosed by the nucleus. 



4. As division progresses, the central-spindle becomes three 

 or four times as long as it is in the metaphase. 



5. The karyosomes break up, by repeated division, into 

 innumerable chromatic elements. In some cases beaded fibers 

 are formed by the linear arrangement of larger chromatin 

 particles. These fibers are the only indication in Noctiliica 

 of a spireme-stage. The chromatin elements begin to form 

 the chromosomes, which, at first, are lines of single granules 

 extending from the nuclear membrane on the side next the 

 sphere towards the opposite side. At this stage they appear 

 like radial-fibers extending around the central-spindle and 

 forming a nearly closed ring. This incomplete ring of chro- 

 mosomes is the nuclear plate. 



6. The chromosomes next become thicker, especially at the 

 ends next the central-spindle, and, probably, by the aggrega- 

 tion and fusion of the granules. This enlargement continues 

 towards the opposite ends, until, finally, the chromosomes are 

 of uniform thickness. 



7. The chromosomes divide longitudinally and while lying 

 in the nuclear plate. The halves then separate, beginning at 

 the proximal ends. 



