152 



AN INTRODUCTION TO ZOOLOGY. 



The Actinozoa owe their flower-like appearance to 

 their tentacles, which, as already stated, are arrangred 



spore being tlie name given to vegetable structures witli hard 

 coats, which are like seeds, only produced asexually, that is to 

 say, without undergoing any process of fertilization. The 

 spore, falling on any damp surface, splits and germinates, 

 exactly like a seed, and from its growth there is developed 



the sexual generation of the 

 fern — a small, flat, green leaf, 

 called the prothallium (or frond- 

 let), which has small hairs for 

 roots, and has on its lower sur- 

 face hollow oases of two kinds, 

 called anthnridia and arche- 

 gonia, which respectively con- 

 tain the male cells, antlierozoids 

 (animal-like male bodies, so 

 called because they have the' 

 power of moving about, which 

 they accomplish by means of 

 their active cilia) and oospheres, 

 Pig. 31.— Alternate generation of a or egg-cells. From the 00- 

 fern; prothalliuni or sexual plant, spheres, fertilized by the 

 Under aide ( x 10) : ar, archegonia ; '^ , '' 



an, antheridia: li, root-nairs. (From antherozoids, there are de- 

 Prantl and Vines' " Text-boot of , i ■ . . » 



Botany"). veloped in tiirn specimens oi 



the fern. The large fern and 

 the small green leaf, or prothallium, are spoken of re- 

 spectively as the sporophore (spore-bearing) or asexual 

 generation, and the oophore (egg-bearing), or sexual genera- 

 tion of the fern. In certain more highly specialized forms 

 of the vascular cryptogams, it is found that these prothallia 

 are very much reduced in size and importance, so that some- 

 times they only just project from the spore; while they are 

 also distinguished into two sorts, those which bear only 

 antherozoids and those which bear only oospheres. The 



