IGO 



GK-XKRAL PRIXCITLKS OV ZOOLOGY 



Even the dincrciice in niclalinlisni is Iiv no means snfl'ieienl. I'".\'erv plant 

 has a iloulile exehan,L;e ul material. In ils mo\emenls and ollu-i" \ilal I'unelicms 

 the xeijetalile jinUoplasm [ii'odiiees earlion dioxitle and eimsiimes (i.wijen; al llio 

 same time lliere goes on, uiidia' llie inlUR'nee of snniiglil and vi clilorophyl, llie 

 reduction of carhon dioxide and llie giNini; olT of ox\\gen. In cliloropliyl- 

 ConlaininL; plants the redueing process pi-e]ioiidcrates so considcraM)' during ihc 

 day that the\' gi\'c olT a (|uainit\' of ox\gen, and onl\- at niglu, \\ lien the reducing 

 process becomes iiUerrupled on account ol the lack of .sunlight, docs the pro- 

 duction of carl)onic-acid compounds hecome j.crceplilile. ]!ut il the clilorophyl 

 be al.isent the reducing processes disappear; chlorophylless fungi ami bacteria 

 have, therefore, the same mettibolism, so far tis carbon dioxide is concerned, as 

 animals. So also it is incorrect to sav that onlv |ilants ha\e the power to make 

 cellulose, for cellulose is fouml in many lower animals, the rhi/.opod.s, in the 

 highly organi.^ed grouji of lunicates ami t'\en among the ;irlhropods. 



Morphological Distinctions. — I'urning to the morphological characters, 

 multicellular animals and multicellular plants are readily distinguished, since 

 the former in the germ-layers have a jirinciple peculiar to them; with the a])pear- 

 ance of the gastrula each organism is undoubledU' an animal. Hut in unicellular 

 animals the arrangement of the cells is lacking, ami only the cimstitution of the 

 single cell can guide us. Now arc there unmistakable morphological dilferences 

 between the animal and the \-egelable cell? 



Plant-cells have a Cellulose Membrane. — In the structure of ]ilant and 

 animal cells an important distinction is found in the fact thtit the former has a 

 cellulose membrane, but the latter is usuallv membrane- 

 less. To tliis distinction nnist be relerred in the last 

 analysis the wiilely different ajipearance of the two 

 realms. Since the plant-cell is early surrounded with 

 a iirm coat, it loses a large jiarl of its power of further 

 changing its form; hence \egetable tissues and organs, 

 in spile of the manifold intracellular differentiations, 

 like the chlorophyl granules, are uniform in coni])arison 

 with the inconcei\'able nniltiformity \vhich animal 

 structures disclose. The higher stages of organization 

 wdiich the animal kingdom reaches, e\en in ils lower 

 classes, is in great part the result of the fact Ihtit the 

 cells of animals do not become encapsuled, but ha\e 

 preser\ed the ca]iacity for moi'C varied and higher de- 

 \elo]mient. but e\'en here transitions are hmiul be- 

 twei-n the lower ])lants and animals. In the lower 

 .\!ga' the ci-lls can lea\'e their cellulose membrane, and 

 swim about freely ((ig. i lO), before thev enclose them- 

 seKes tiiu-w. (,)n the other hand, most unicellular 

 animals encyst; they pause in their ordinary functions, 

 bec(mie sjiherical, and surround themseh(.s with a firm 

 membrane, sometimi-s exeii of cellulose. Since in both 

 ctises an alternation between the encapsuled and the 

 b'ce condition occurs, only the longer duration of the 

 d to a ilislinctiiui. liiU hei-e occurs the possibility 

 tliat indilTerent intermediate foiaiis exist; their aclutil I'xistenci- pre\cnts, e\en 

 yet, a sharp distinction l)et\\een the animal and \egetable kingdoms. 



'^ 



I'lO. Il6. — <.]uhii[ii- 

 nilim ill sporc-fornialioa 

 (after Saelis). . I , a piece 

 of Ihc alga willi t'sea|)- 

 ing CL'll-eonK-ils: J\ 

 zoospore foriiird from 

 llu' contents; t ', /.oospore 

 lixeil anil i/eriiiinalintr. 



oni' or of the other can le 



V. GROGR.\riirC,\L DlSTRlIiUTION OF .VNIMM.S. 



The Different Faunal Regions. — b'ven a superlicial knowledt'c of the 

 distribution of animals shows that the animal populaticm, ihc Jdniui, in different 



