(ECOLOGY. 



I 99 



numerous individual animals which depends upon an organic 

 bodily connection; the latter may arise in two ways: first, 

 by animals originally separate approaching one another and 

 partially fusing together; secondly, by animals formed by 

 division and budding remaining united with one another 

 instead of separating. The first case is extremely rare, and 

 in the animal kingdom plays no role \vhatever. 



Colony Formation by Fusion. Many protozoa fuse 

 with one another and form larger bodies in which the indi- 

 vidual animals can still be recognized. Among the multi- 

 cellular animals, that of Diplozoon paradoxum is the only 

 case known where animals (Diporpa) normally two (Fig. 

 105), sprung from different eggs, unite into a double animal 

 which recalls certain double monsters, as for example the 

 Siamese twins. 



FIG. 105. Development of Diplozoon paradoxum. (From Boas ) (i) Larva, from which 

 comes (2) '' Diporpa." (3) Two Diporpse uniting. (4) The Diporpse have united into 

 Diplozoon. ;, mouth ; d, digestive tract ; Si, posterior clasping apparatus ; t>, ventral 

 sucking-disk, which serves for attachment to the dorsal cone, r. 



Colony Formation by Incomplete Division and Bud- 

 ding. In general it can be said that the important in- 

 stances of colony building occurring in nature rest upon 

 incomplete division or budding. An animal has the power 

 of asexual multiplication; but this does not go on to 

 the normal conclusion, since complete separation is not 

 accomplished, though indeed two or more individuals are 

 formed. There persist more or less extensive bridges of 

 tissue, which unite the divided parts with one another, 

 or the buds with the mother. The marine colonies of 

 corak and Iiydroids (Fig. 88) may consist of thousands of 

 individuals which, by repeated incomplete budding or 



