ZOOSPORES. 



[ 694 ] 



ZOOSPORES. 



ZOOSPORES. The name given to the 

 ciliated active gemmae or GONIDIA produced 

 from the contents of ordinary or special 

 cells of the Algae, apparently without any 

 previous process of fertilization. These 

 bodies are generally discharged from the 

 parent-cell in the state of PRIMORDIAL 

 UTRICLES, and acquire a cellulose coat 

 subsequently, when they cease to move, 

 and settle down to germinate and pro- 

 duce a structure resembling the parent. 

 In some cases (in HYDRODICTYON nor- 

 mally, in many other Confervoids abnormally) 

 they become encysted within the parent- 

 cell ; and it appears most probable that the 

 small cysts with dense (and often spinulose) 

 coats, such as occur in Spirogyra (PI. 5. 

 tigs. 24, 25) and other genera under certain 

 circumstances are of similar origin, but 

 intended to pass through a season of rest. 

 [In the VOLVOCINE^E, zoospore-like bodies 

 form the permanently active individuals of 

 the families.] 



True zoospores occur pretty generally 

 throughout the Confervoid Algas (with the 

 exception of Oscillatoriaceae, Nostochaceae, 

 and perhaps Diatomaceae), and are described 

 under the heads of the families or genera. 

 A brief review may be permitted here. The 

 largest form is that produced in the apices 

 of the filaments of VAUCHERIA (fig. 801) ; 

 it is ciliated all over, and very unlike that of 

 any other genus. In CEdogonium (PL 5. 

 fig. 7 c & fig. 816) the zoospores are formed 

 out of the whole contents of a cell, and have 

 a crown of cilia around the transparent 

 'beak.' In other Confervaceae, as Clado- 

 phora (PI. 5. fig. 13 c, d), Conferva (PI. 

 5. figs. 10 b, 11 c ) ; in Chsetophora- 

 ceae, as in Cheetophora (PL 5. fig. 9), 

 Draparnaldia (fig. 183, page 216), Stigeo- 

 clonium (PL 5. fig. 5 c c); in Ulvaceae, 

 Ulva (PL 5. figs. 2b,3c, d), Enteromorpha 

 (Fl. 5. fig. 46), in Protococcus (PL 3. fig. 2 b), 



. 



Fig. 816. 



b 









Zoospores of CEdogonium. a have lost their cilia ; and 

 in b germination is more or less advanced. Magnified 

 200 diameters. 



in ACHLYA, in Desmidiaceae (PL 6. fig. 11), 

 &c., as in all other cases, they are formed 

 either singly from the entire contents, or in 

 small or large number by the segmentation 

 of the entire contents, and mostly break out 

 in various ways, as pyriform bodies with two 

 or four cilia on the transparent beak, moving 

 actively for a time, and then germinating to 

 produce new plants. In HYDRODICTYON, 

 as described under that article, their history 

 is different, though the earlier conditions 

 are analogous. It has been found that zoo- 

 spores of two very different sizes are pro- 

 duced in many Confervoids ; these are called 

 macrogonidia and microgonidia by A. Braun 

 (see HYDRODICTYON), and a different func- 

 tion is supposed to be exercised by the lat- 

 ter by some authors, who. believe they are 

 fertilizing bodies (like SPERMATOZOIDS). 



Zoospores exist in a large proportion of the 

 Algae usually included under the FUCOIDE^E, 

 but which Thuret separates under the name 

 of Phaeosporae, including all the families 

 except the FUCACE.E, DICTYOTACE^E and 

 Tilopterideae, which are (for the present?) 

 distinguished by possessing antheridia and 

 spores proper. The Phaeosporous families 

 bear organs called OOSPORANGES and TRI- 

 CHOSPORANGES according to their form, 

 (usually described in Algological works as 

 " spores "), from which are discharged zoo- 

 spores, agreeing in all essential respects with 

 those of the Confervoids, except that the 

 two cilia are often arranged fore and aft, 

 instead of being both in front. Examples 

 of these are described under ECTOCARPUS, 

 MYRIONEMA,CUTLERIA, LAMINARIA, &c. 



It remains to direct attention to the di- 

 stinction between ZOOSPORES and SPER- 

 MATOZOIDS, which are sometimes confused 

 together. This confusion is rendered more 

 imminent by the manner in which the forms 

 pass one into another. The essential charac- 

 ter of a zoospore is, that when separated from 

 the parent it becomes encysted, and at once 

 developed into a new individual resembling 

 the parent (certain at present obscure excep- 

 tions occur, where the zoospore, after germi- 

 nating, at once discharges new ciliated bodies 

 (zoospores or spermatozoids (?)). 



Spermatozoids are transitory structures; 

 when discharged from the parent-cell, they 

 either make their way to a germ-cell of a 

 spore, fertilize it and disappear; or if de- 

 barred from this, at once perish, without 

 germination. As stated under SPERMATO- 

 ZOIDS, these bodies vary much in form. In 

 the higher Cryptogamia they are spiral fila- 



