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55 



POND LIFE, 113 



kingdoms ; because they enable us to see what are the characters 

 which distinguish living things from not-living things, and because 

 they show us, in simple organisms, laws which will be found 

 carried out in a more complete fashion in the higher groups of 

 plants and animals. 



EXPLANATION OF PLATE XII. 



Figs. 1 — 10. — Reproduction of a Diatom (Cocconeis pediculus, Kg.), 

 after Carter. Two small diatoms, one less than the 

 other (Fig. 1) become united by a mucous-like excre- 

 tion, and the valves open (Fig. 2) ; the contents fuse 

 (Fig. 3) ; become spherical (Fig. 4), and afterwards 

 elliptical in shape (Figs. 5 and 6) ; a line then appears, 

 dividing the spore into two halves (Fig. 8), which com- 

 pletely separate (Fig. 7) ; and in their complete condi- 

 tion are seen in Figs. 9 and 10. 



11. — Volvox glohator, after Nave. 



12. — (Edogonium ciliatum, after Pringsheim. The stem consists 

 of four cells, above which are two large, oval, spore-forming 

 cells. Attached to these are the small, urn-shaped cells, in 

 which the small, moving, fertilising spores are formed. 



13 — 15. — Reproduction of a Desmid (Cosmarium hotrytes), by 

 division, after De Bary. The two halves of the cell (Fig. 

 14j commence to separate a little, and a division (Fig. 13) 

 runs across the intermediate part, which gradually enlarges 

 until two cells, each as large as the original one, are formed 

 (Fig. 15). 



16 — 18. — Conjugation of the same Desmid, after De Bary. Two 

 cells, each like Fig. 16, lie together in a mass of jelly, and 

 its contents protrude (Fig. 17). The contents of the two 

 cells mix together, and form a round spore with a gelatinous 

 wall, beside which lie the four empty halves of the two ori- 

 ginal cells (Fig. 18). The round cell eventually forms in its 

 interior two bodies like the original Cosmarium (Fig. 14). 



,, 19 — 23. — Conjugation of Spirogyra longata, from Sachs. 



A small prominence protrudes from each of two cells lying 

 near each other (Fig. 19). These unite and form a commu- 

 nication between the two cells, through which the contents 

 of one cell passes into and mixes with the contents of the 

 other (Fig. 20). The result is the formation of a spore 

 (Fig. 23), which germinates into a new plant (Figs. 22, 21). 



,, 24. — Nostoc, sp. 



Showing the strings of cells lying in a jelly-like mass. 



,, 25 — 26. — Protamceha Scliidzeana, after Hseckel. 



Fig. 25. — The Amcaha, undergoing division ; Fig. 26. — One 

 of the young Amcehce formed by the process. 



VOL. IV. I 



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