110 



Chlorophycece 



septum appears and cuts off the swollen end as a zoogonidangium. 

 The contents of this gonidangium, which are of a rich green colour, 

 gradually become rounded off, forming an oval zoogonidium of 

 large size. The whole surface of the zoogonidium is usually 

 clothed with numerous short cilia, arranged in pairs, and in the 

 surface protoplasm under each pair there is a small nucleus. The 

 entire structure contains one central cavity filled with cell-sap 



Fig. 42. A and B, portions of thallus of Vaucheria showing formation of septa on 

 injury; A, Vaucheria geminata (Vauch.) D. C.; B, V. sericea Lyngb., from 

 Harefield, Middlesex. C, apex of filament of V. sessilis (Vauch.) D. C., show- 

 ing the zoogonidangium from which will escape a single zoogonidium. D, ger- 

 mination of the zoogonidium of V. sericea, from E. Yorkshire. E, V. sessilis 

 from W. Yorkshire, showing developing oogonium (on right) and antheridium 

 (on left). F H, V. geminata (Vauch.) D. C., from Barnes Common, Surrey, 

 showing development of sexual organs. (All x 75.) a, antheridium, 06, oogo- 

 nium; zg, zoogonidangium. 



which is traversed by strands of protoplasm, and Schmitz has 

 pointed out that it can be looked upon as an aggregate of zoogonidia 

 with a great resemblance to certain of the more complex members 

 of the Volvocaceae. This compound zoogonidium escapes by an apical 

 opening of much smaller diameter than itself and through which it 

 pushes its way. Sometimes, owing to the rotatory movement of the 

 cilia, the part first exuded becomes separated from the portion still 

 left in the gonidangium and two zoogonidia are formed instead 

 of one. 



The zoogonidia generally escape in the morning, that is to say, 

 after the plants have been in the darkness for some time. They 



