448 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Cytology of Rabbit. * — Dr. Hans von Winiwarter has used the 

 epiploon of foetal and newly-born rabbits, and the amnion in the same 

 animal, in the study of the intermediary body (corps intermediaire, 

 Zwischenkorper) and of the chromosomes. He finds that at the diaster 

 stage no trace of the structure known as the cellular plate appears, 

 but a little later swellings appear on certain of the achromatic threads. 

 As the daughter-cells separate, these swellings fuse together aud form 

 the intermediary body. In the amnion the intermediary body forms 

 a spherical body in a clear space, instead of being fusiform as in the 

 epiploon. In both cases, however, it clearly arises from the union 

 of fusiform thickenings (the cellular plate) formed on the threads con- 

 necting the daughter-cells. These thickenings the author believes to 

 originate by the confluence of microsomata, which, during the process, 

 undergo chemical changes, manifested by changes in their staining re- 

 actions. As the swellings on the spindle threads fuse to form the inter- 

 mediary body, this should be regarded as a rudiment of a cell-membrane, 

 rather than (as Flemming supposes) as the homologue of the cellular 

 plate of the plant-cell. 



In regard to the number of the chromosomes, the author finds that 

 the number 42 is most common, and is probably tho typical number for 

 somatic cells, as also for young sexual cells. Mature ova, however, 

 appear to contain 20-24 chromosomes, or 10-12 after the formation of 

 the first polar body. A similar condition has been described for Ascaris 

 by Boveri, and possibly also occurs in man. 



Giant Nuclei.f — Prof. E. Ballowitz finds that the membrane of 

 Descemet in the cornea is an excellent object for fine histological 

 work. Pending the publication of a paper on the subject, he notes as 

 of special interest the occurrence there of giant nuclei. The cells of the 

 membrane contain very largo spheres, with a microcentrum containing 

 2-4 central corpuscles. Under the influence of the sphere the nuclei in 

 post-embryonic life undergo a series of chauges, losing their original 

 rounded shape, and becoming kidney-shaped, semi-lunar, horseshoe- 

 shaped, and ultimately S-shaped. Scattered among the ordinary nuclei 

 others occur which are 1^-3 times as large, but undergo similar changes. 

 They occupy giant-cells which occur sporadically among the other cells, 

 and do not apparently differ from those, except as regards size. The 

 phenomenon may be regarded as analogous to the sporadic appearance 

 of giant spermatids or spermatozoa among those of ordinary size ; this 

 has been described for various animals by different observers. It may 

 be a nutrition phenomenon, and is possibly associated with pluripolar 

 mitosis. 



c. General. 



Thalamencephalon of Reptiles.:}: — Prof. L. Edinger continues his 

 study of the Reptilian brain, and describes the region of the thalamen- 

 cephalon. The thalamus proper is distinguished from the dorsal epi- 

 thalamus, and both from the ventral hypothalamus, and these parts are 

 described in detail. The brains of about 17 species have been studied. 



* Arch. Biol., xvi. (1900) pp. 685-707 (1 pi.). 



+ Anat. Anzeig., xvii. (1900) pp. 340-6. 



X Abhaudl. Seuckenberg. Nat. Ges., xx. (1899) pp. 161-96 (3 pis.). 



