320 



SCIENCE-GOSSIP. 



THE EVOLUTION OF THE ANIMAL CELL. 



'TPHE processes, explained in the last portion of 

 this article, which a complete cell in the 

 tissues of the fully-formed animal undergoes in the 

 struggle for existence, present a very interesting 

 feature in the disposal of the worn-out material. 

 The absorptive and eliminating power of the proto- 

 plasm is in affinity with the process, which, how- 

 ever, is a feature of the adult cell amongst fully- 

 formed individuals, and may be well understood 

 from a perpendicular section from some portion 

 of the human body. " It must be remarked that in 

 equal bulks of the tissue there is a larger quantity 

 of the germinal matter in the lower part than in 

 the upper part, which is a long distance from the 

 nutrient surface, and that the converse is the case 

 as regards the formed material which gives to the 

 tissue its properties and physical characters" ( 1 ). A 

 feature worthy of diligent attention is the apparent 

 increase of the cells as they progress, until about a 

 medium distance is arrived at, when from that 

 point they noticeably diminish. While again, " the 

 distance between them increases on account of the 

 increased formation and accumulation of formed 

 material ; so that by the time the cells have reached 

 the surface the distance between the masses of 

 germinal matter is reduced again by the drying 

 and condensation of the formed material " ( ll ). 



The changes which the living cell passes through 

 may be briefly considered to be at the base, and in 

 close contact to the nutrient surfaces are " masses 

 of germinal matter embedded in a soft mucus-like 

 and as yet continuous formed material." The 

 germinal masses divide, and each absorbs some of 

 the surrounding mucous mass to compensate the 

 matter thrown off in the oldest cells. Each mass 

 continues to increase in size according to the 

 quantity of nutritious pabulum absorbed, which 

 passes through the stratum of formed material, a 

 portion of the germinal matter undergoing during 

 the process conversion into formed matter, which 

 accumulates upon the surface within that already 

 formed. As each new layer is deposited upon the 

 surface of the germinal matter, those layers of 

 formed material are stretched, and with them the 

 last developed are more or less incorporated, the 

 germinal matter increasing for a time while the 

 newly-formed matter is evolved. Now, as progress 

 is made, the new cells being produced below matter 

 which has thus been formed, it — the matter — is 

 gradually removed further from the nutritious and 

 vascular system, and consequently as the material 



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



{Continued from page 290.) 



so formed becomes older, it is less sensible to the 

 process, assuming on that account a harder nature, 

 which makes it less permeable to the nutrient 

 elements, and from this point it ceases to increase 

 in size. Germinal matter decreases on account of 

 its conversion into the solid or formed material 

 which results ; hence the further it — the material 

 — is from the nutritious germinal surfaces, the 

 less benefit does it derive from the surroundings, 

 because of the impotency of the harder and denser 

 mass to absorb pabulum in corresponding ratio. 

 The result is that the germinal matter — the 

 nucleus — becomes smaller in old age, so that 

 eventually the element of germinal matter left 

 unconverted into formed material, being unable to 

 sustain life further, dies, and the cell having arrived 

 at the surface is cast off, a "mass of perfectly 

 passive, lifeless, formed material." 



The peculiar substance which constitutes the 

 bodies of unicellular organisms was named ( 2 ) 

 ' ' sarcode " on account of the mechanical or irritable 

 movements which it was capable of undertaking, 

 and which gave rise to the assumption that the 

 sarcode was a differentiated material. This 

 assumption induced many naturalists to endeavour 

 to demonstrate the structure of the sarcode to be 

 a combination of many cells, with the view of 

 bringing this material under, and including it in, 

 the cell theory ( s ). Cohn was the first to compare 

 the sarcode with the protoplasmic contents of the 

 plant cell, consequent on his observations on the 

 similarity of vital phenomena, and these obser- 

 vations led De Bary, Haeckel, Max Schultz and 

 others ( 4 ) to follow the matter further in detail. 

 The result was to demonstrate beyond doubt 

 that sarcode, in vegetable and animal cells, was 

 identical with protoplasm. Protoplasm then, that 

 interesting substance so mysteriously endowed 

 with vital properties, forms the basis of cell 

 evolution. Protoplasm it is in the beginning, 

 and protoplasm it remains to the end, since 

 in assuming any change or changes it ceases 

 to be protoplasm. This feature is one of the 

 most interesting problems of cell evolution or 

 development, for did the protoplasmic substance 

 remain so and not experience any changes, then no 

 development or evolution would result. On the 

 other hand, this organic mass will necessarily cease 



(') Beale : " Protoplasm 

 (1*) ibid. p. 24. 



Life Force and Matter," p. 24. 



( J ) Dujardin. 



i 3 ) Cohn : " Nachtrage z. Naturgeschichte des Protococcus 

 pluviatalis." Nova Acta, vol. xxii. pp. 607-764. 



( 4 )Mas Schultz : " Das Protoplasma der Rhizopoden und 

 der Pflanzengelle." De Bary : Myxomyceten Zeitschrift f. 

 Wissenchalftl. Zool., 1859. Haeckel: Die Radiolarien, 1862. 

 Die Moneren. 



