ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 655 



chromosomes formed by the second longitudinal splitting in the first 

 mitosis. 



There is thus no " reducing division." The only reduction which 

 occurs is effected in the germinal vesicle, and the chromatin destined to 

 form the chromosomes of the polar divisions is diminished in bulk 

 merely. 



Ccelentera. 



Increase of Mesenteries in Madrepora.* —J. E. Ducrdeu finds that 

 in most of the polyps of Madrepora only the six bilateral pairs of 

 primary mesenteries are developed, four pairs complete, two incomplete. 

 On any colony a few enlarged polyps may have more. The new mesen- 

 teries beyond tho primary six pairs are added in complete or incomplete 

 bilateral pairs at only the two axial extremities, the entoccele of the 

 dorsal and ventral directives. Like Porites, Madrepora illustrates the bi- 

 lateral entoccele type ; the cyclic disposition is never assumed ; the 

 directives form isocnemic pairs, but the other pairs are all anisocnemic. 



The pinnate method of mesenterial increase is distinct from that 

 chaiacteristic of most recent corals; in these the metacnemes are added 

 in isocnemic pairs all round the periphery of the polyp, within the six 

 primary exocceles, and in the end constitute one or more distinct alter- 

 nating cycles. In Porites the same method of increase is characteristic, 

 except that in any one polj-p of Porites the new mesenteries are disposed 

 at either the one or the other extremity, not at both. 



Six new bilateral pairs of mesenteries appear practically simulta- 

 neously iu Madrepora, but only later do they all extend down the 

 poly pal wall. In Porites the new pairs follow one another in regular 

 succession. 



In Madrepora the mesenterial increase is early associated with 

 fission of the stomodaeum, and in the end probably with complete 

 polypal fission, in which half the mesenteries of each tission are derived 

 from the primary twelve of the original polyp, and the other half are 

 new formations. The resulting paired arrangement of the mesenteries, 

 including the presence of two pairs of directives, is exactly as in primary 

 polyps. Fission of the stomodaaum appears very late in Porites, after 

 full establishment of six new pairs of mesenteries. 



Regeneration in Tubularia. f — B. Godlewski gives an interesting 

 description of the regeneration of Tubularia mesembryanthemum when 

 the stem is cut in two longitudinally. The hydranth may re-develop 

 simultaneously at both ends, or only at one end (which may be aboral), 

 or in the middle of the stem (in pieces cut lengthwise unsymmetrically). 



Regeneration in Hydra. X — U. T. Rowley has sought to discover 

 whether, during the period of regeneration, the old cells go over without 

 change into the tissue of the new animals, or whether new cells are 

 formed, and if so, in what part or parts. The answer given is that the 

 new cells which appear during the regeneration are formed by division 



* Johns Hopkins Univ. Giro., xxi. (1902) pp. 59-66 (12 tigs.); Ann. Nat. Hist., 

 x. (1902) pp. 96-115 (12 figs.). 



t Bull. Internat. Acad. Sci. Cracovie, 1902, pp. 3S7-96 (11 figs.). 

 X Ainer. Nat., xxsvi. (1902) pp. 579-83. 



