SCIENCE-GOSSIP. 



347 



i of Ehrenberg, for some reason or other 

 he did not retain the specific name. The genus 

 r .■•-< was established by Ehrenberg, and 





Fu. -. — - kjs cuchlora (x 500). 



placed by Dujardin in the family Thecamonadiens, 

 which he characterizes as follows : "' Thecamona- 

 diens. — " Animaux ordinairement colores, revetus 



d'un tegument non-contractile, membraneux on dur 

 et cassant, et n'ayant pas d'autres organes loco- 

 moteurs qu'un ou plusieurs filaments flagelli- 

 formes." Owing to the fact that the various 

 genera had only one feature in common, namely, 

 the possession of a non-contractile sheath or lorica, 

 they formed a most heterogeneous and unnatural 

 assembly. The family was finally pulled to pieces 

 by Stein in his " Organismus der Infusiorthiere." 

 abtheilung iii. heft i. (187S), who, recognizing the 

 affinity of the genera Trachelomonas and Eitglena, 

 placed it among the Euglenidae. 



{To be continued .) 



THE EVOLUTION OF THE ANIMAL CELL. 



By Joseph Smith, M.R.I. A., F.L.S. 



(Concluded from page 321.) 





XT I'CLEI in animals appear in the form of 

 rounded objects, and are situated in the 

 middle of the cells, but in some classes of cells, 

 such as lymph corpuscles, etc., and in the epithelial 

 cells of the gills of salamander larvae, no nuclei can 

 be distinguished during life or until coagulation of 

 the parts takes place, or until the parts have been 

 submitted to the action of weak acids for the purpose 

 of bringing the nuclei up. Amongst the lower 

 organisms the nucleus may assume various forms, 

 sometimes the form is that of a horse-shoe, as in 

 some of the Infusoria, or of a twisted strand, as in 

 the Vonicellae. 



Another peculiarity of this object is, that the 

 greater the bulk of protoplasm, i.e. material sur- 

 rounding it, the larger the nucleus becomes. As a 

 rale, amongst animals and plants one nucleus 

 exists to each cell, but many of the lower organ- 

 isms, such as the Infusoria, Myxomycetes, etc., 

 are exceptions to it, possessing many nuclei in 

 their cells They are so minute as to be invisible, 

 especially in the cells of the Myxomycetes, wherein 

 tbey can only be distinguished by a special method 

 of staining. The nucleus is made up chiefly of two 

 constituting materials, nuclein or chromatin, and 

 paranuclein or pyrenin, and these can be 

 distinguished under a sufficiently powerful lens. 

 The preponderating material in the nucleus is the 

 chromatin, and it is the 



Nuclein or chromatin is present in the beads of the 

 spermatozoa. Paranuclein i . a! a ; 



e presence in tl. fails, 



What . et arc and th<: manner of its vital 



>le tins 

 sobsta: 1 bai t'' 1": 



worked out It. of all 



tfkallne 

 solution, solution of salt, sulphate ol i";. 

 etc., which caov- is, when treated with 



any of them, to swell up. It is considered that 

 nuclein and paranuclein form the two essential 

 constituents of the nucleus, but besides these 

 essentials, there are present linin, nuclear sap and 

 amphipyrenin. The vital functions of these 

 materials are less important, the linin forming the 

 thread-like structure which frequently is seen in 

 the nuclear cavity. The nuclear sap, generally 

 present in large quantities, fills up the interstices 

 left in the structures composed of linin, nuclein 

 and paranuclein, and it is evidently functional in 

 nourishing the nucleus. 



Amphipyrenin is the term which has been 

 applied to that substance, which forms the 

 separating membrane of the nucleus from the 

 protoplasm. This substance is as difficult to 

 demonstrate as to settle the vexed question, 

 whether the larger number of cells are enclosed by 

 a membrane or not. It is, however, easily 

 distinguished in the large germinal vesicles of 

 many eggs, especially thoseof amphibians, wherein 

 it is also somewhat dense, and on this account the 

 nucleus can be extracted from immature eggs with 

 facility. In other instances it is questionable 

 whether any membrane exists, and Flemming (') 

 has failed to discover it in the blood of amphibians. 

 Hertwig has also been unsuccessful in discerning it 

 in sperm mother cells of Nematodes in a certain 

 I development. Nuclein may manifest its pre- 

 ^i the form 1 1) fini granules, as lai ge ma 1 le i, 

 as fibrils, as a framework, 01 In the form oi honey 



1 an I 'Iim in 1 the 1 88 oi the vital 



thei .'il' itani e 



In formulating a definition >>f ilic nucleus, its 

 shape in >< itbi d I'begreal diffii tilt] lies 



ital tail 11 d In It, 



exactly as in defining the cell, the greati I difficulty 

 ■ ribing the prol i i he nu I 



•llthi Leipzig, iBSa. 



3 



