INVEKTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 409 



(1) Tlie number of cells increases in geometrical ratio. 



(2) The rate of multiplication increases ; tbis increase is, liowever, 

 counteracted by tbe dcatb and loss of a portion of tbc cells (e. g. 

 epidermis). 



(3) The interval between the birth of two successive generations 

 contiiiuallii increases. 



(4) The iveight of the cells diminishes at every division and again 

 increases until the cells regain approximately their original size. 



(5) The weight of the cells may alter in one direction during several 

 generations. 



(6) The same cell may vary in weight. Tbis may be due to tbe 

 normal activity of tbe cell (salivary and pancreatic c. g.) or to tbe 

 decrease or increase in tbe amount of water or fat. 



By tbe aid of a formula based on tbesc laws tbe autbor finds tbat 

 tbe number of cells is determined by tbc ratio of multiplication and 

 tbc frequency of division, wbile tlie average weigbt is determined by 

 tbese two causes and by tbe weigbt of tbe cells, and tbc loss of cells. 

 Tbe probable fact tbat tbe i-ate of growtb in weigbt increases for 

 about balf tbe period of growtb, tben remains constant, and finally 

 diminislics to zero, is interpreted by saying tbat at first tbe increment 

 of senescence is less tban tbe increment of tbe number of cells at cacb 

 division ; soon tbe former surpasses tbe latter, till growtb eitber 

 ceases or only counterbalances tbe loss of cells ; wben tbe rejuvenating 

 power is exbausted tbe sexual j^roducts are developed. 



Animal Cellulose.* — Herr A. Francbimont bas examined some 

 Tunicate tests witb tbe view of ascertaining wbicli of tbe sugars is 

 jiroduced from tbem. By trituraliug tbe carefully cleaned tests witb 

 concentrated snljiburic acid and leaving tbem in it for twenty-four 

 liours, a liquid was obtained wliicb wben diluted witb water exbibited 

 dextral jwlarization. On boiling tbis, and saturating witb barium 

 carbonate and cxjiosing to steam, a crystallized substance appeared 

 after some weeks, wbicli presented precisely tbe ajijicarance of glucose 

 obtained from vegetable cellulose by tbe same metbod. I'or tbc 

 I)resent, tlicrefore, be would regard tbe sugar as ordinary glucose, 

 awaiting tlie result of fiirtber investigation. It is still possible 

 tliat tbe molecular relations of tunicin differ from those of cellulose ; 

 in otber words, tbat tbe radicle C-.HioOo is present in different 

 proportions in tbc molecules of tbe two ; and tbat tbus isomerism 

 may explain tlic differences, if tbcso exist, between tbe two com- 

 pounds. 



Influence of Light on Animals.t — In this interesting note, Molc- 

 Bcbott and Fubini jtoijit out bow little this subject bas been as yet 

 investigated. Herr Scbeiuik appears to liavc undertaken some ex- 

 periments; oggs ol' Rana tcmporaria and Bnfo ritirreus were placed 

 in vessels and covered witb glasses or fiuids of difi'erent colours; the 



* ' Bcr. Dciitsch. Clioni. rjcsoll.,' xii.; htc ' Nfttiirfoiscli<r,' xiii. (18S0) p. 0(5. 

 t ' ITiiti r.siK'li. Ndtiirlclirc Mciiscli. niul Tliiorc,' xii. p. 'idt! ; stv ' Nntnrforschcr." 

 xiii. (18K0) p. ll;!. 



VOL. III. 2 E 



