PRO* 1 .- AGASSI2TS 



ascertained that the animal tissues are. in their 

 fundamental structure, identicalwith the vegetable 

 tissues,. we may expect that l>eianical investiga- 

 tion may tlnow as much light upon the animal 

 kingdom, as the study of animals may threw upon 

 the vegetable kingdom. 



Easy as it has- been- to study- the s-tractt8 of 

 vegetable tissues, so diScu-lt has it been to ascer- 

 tain their functions to ascertain the working of 

 the various organs 5fl plants The most different 

 and contradictory opinions are entertained upon 

 vegetable functions, upon the circulation of their 

 sap, upon their respiration, and the actin of res 

 piratibn upo-n their fluids. 



On the contrary, in animal structures, tfae func- 

 tions are easily traced 1 . The combined action of 

 various functions upon each other, can be easily 

 asct-rtained It was the stractare the intimate 

 stiuctwe vvhii-h it wasd'ificult to investigate. And 

 now, by re 1 erring the result fiora one kingdom to 

 the other, it is to be hoped that much more rapid 

 progress will be obtained than before. 



One unexpected resnlt has airead'y been ascer- 

 tainednamely, that cells are properly the organs 

 of living beings; that all functions are influ- 

 enced by life, by the independent life of isolated 

 cells. It is not the stomach, as a whole, which di 

 gests; digestion is influenced' by the cells which 

 line the internal surface of the stomach. 



The life of individual cells may be compared to 







the action of several Farce organs combined into 

 one system, as a whole. Ifow much independence 

 there is really in the life of individual' cells, can no 

 where be better shown thaa in some of the germs 

 &f Moll asks. 



Let me for a moment illustrate the various figures- 

 which are represented in Plate XL. 



They show the changes which a Mollnsk may 

 undergo; a species of Eolis, a naked Mollusk, 

 found in Boston harbor, of which tkere is a figure 

 in Plate XLIT. fig. C Several species of these 

 Mollirsks occur in Boston harbor, and can at any 

 rime be obtained far investigation. Several eggs 

 which contain a single yolk, are first noticed 

 ((Plate XL), and in tiie same plate are represented 

 all the changes whrch the yolk undergoes in the 

 process of dividing, up ro the period when the 

 whole mass of yolk is transformed into ranumer- 

 able cells, as represented here 



The divisions of these masses are not always so 

 reeulai? as thay havg been described. In this 

 Eolis, it does not constantly tak'e placeby a reg- 

 ular division iatotwo halves. "?ou see that the Swo 

 halves are more or less different in their size; 

 sometira-es the division takes place into three 

 spheres, two of which are srailer than the other, 

 and not even equal among themselves-. In others, 

 there are th-ree equal spheres 5 in others, fou-? cq,ual 

 spheres ; in others are four less equal; in oShers 

 are five almost equal ; aad still in others, five, all 

 f which are small. Many irregularities ocour. 

 Ihers is tia invar iable 



|Pr ATE XL CHANGES OF THE YOCTNG 



[.PLATE XLII J 



You iiiav 



ures ot ibe &aine, 



('Plate XL) that the process of dividing the yolk 

 is very regular, there being first two, then four 

 equal divisions, out of which may arise on one 

 side QUE ottn.es large spheres, and on the 



