THE LOWER FORMS OF LIFE. 103 



their cilia, become at length fixed, and after a time have the appear- 

 ance of flattened discs (Fig. 131) surrounded with a close fringe of 

 cilia, and showing a tendency to divide in four places. This disc 

 becomes, in fact, the root or hydrorhiza, and from the centre is 

 developed the first polypite (Fig. 132), which by budding grows into 

 the tree-like Zoophyte or coralline which we pick up on the sea- 

 coast, and magnified drawings of which I have given ante, pp. 79, 

 81, and 82. While the facts connected with the reproductive 

 phases just described are fresh on the memory, let us follow out 

 the life history of one of the Medusididae. 



It will be remembered that, in describing these forms in the last 

 chapter, I pointed out (i, Fig. 120, p. 95) a swelling in each of the 

 radiating canals just before it terminates in the marginal canal. This 

 is the reproductive body, which contains the eggs or embryos. These 

 when first emitted are covered with a gelatinous investment, and 

 have the appearance shown at Fig. 133, but which in a free con- 

 dition are like Fig. 134. The product of one of these eggs is an 

 animal known to naturalists as an hydra-tuba, and in its early or 

 very young state is represented at Fig. 135 with four marginal 

 tentacles in the process of development. In a short time these 

 tentacles become doubled, and the creature fixes itself by its hydro- 

 rhiza, as seen in Fig. 136. The mouth now becomes enlarged, the 

 tentacles again divide, and the creature becomes, in fact, as nearly 

 as possible a fac-simile of the fresh-water Hydra (Fig. 137), in which 



Fig. 133. Fig. 134. Fig. 135. Fig. 136. Fig. 137. 



condition it may remain for years, budding and sending off young 

 Hydree exactly as the Hydra does. But all this time it is only in a 

 transitional condition. We must not forget that we are talking now 

 of the product of an egg deposited by one of the large Medusae, or 

 so called " jelly fish." 



The intelligent reader will also remark that while the corallines 

 in their development pass through the form of Medusae, these latter 

 return the compliment by assuming the form of the polyp. This 

 constitutes what is termed parthenogenesis, or alternation of genera- 

 tions, in which the child is never like its parent until it has passed 

 through a period of existence of indefinite length, during which 

 period it gives birth or origin to other beings like itself, all of which, 



