i6 



HISTOLOGY 



Each animal lives at the end of its stalk independently of the others 

 / of the body. It secures 



its food by means of its 

 own ciliary movements 

 and carries on for itself 

 all metabolic and repro- 

 ductive functions inde- 

 pendently of the colony 

 as a whole. 



An Example of a Col- 

 ony of the Second Order : 

 Gonium pectorale. A 

 specimen of Gonium 

 pectorale is always com- 

 posed of sixteen oval 

 cells attached laterally 

 to one another in such 



FIG. 14. Gonium pectorale, showing the individuals. (From a manner as to form a 



square colony with 



twelve cells on the margin of the square and four cells inclosed by the 

 lateral ones. The 

 entire colony is 

 surrounded by a 

 gelatinous sheath. 

 Each cell is oval 

 and inclosed within 

 a cellulose wall. 

 The cytoplasm con- 

 tains a cup-shaped 

 green chloroplast 

 and a centrally 

 placed nucleus. 

 Near the open mar- 

 gin of the chloro- 

 plast there is a 

 bright red stigma. 

 In the cytoplasm 

 opposite the open- 

 ing of the chloro- 

 plast are two 

 contractile vacu- 

 oles. From this 



FlGg J S' Volvox globator, a colonial organism of the third order. 

 (From WILSON, after J. H. EMERTON.) 



same region of the cell two slender flagella are given off (Fig. 14). 



