POLYPIFERA. 



are ascertained to be the eggs, or gemmules of the fu- 

 ture animal. In a few months they enlarge in size, and 

 assume an oval, or pear-shaped form, and Fig. 2. 

 are covered with cilia, or hairs, as shown 

 by Fig. 2. They then become detached 

 from the parent, one after another, and 

 float or swim along with the current, always 

 carrying their broad and rounded extremity 

 forward. While thus suspended in the 

 water, the cilia, with which they are cover- 

 ed, are in rapid and perpetual motion, giving them a 

 slow impulse forward. In these movements if they 

 strike against each other, or meet with any other im- 

 pediment, they avoid the difficulty as other animals do, 

 by turning aside and then proceeding in their former 

 course. In some instances when two of these little 

 animals happen to meet, they adhere to each other, and 

 in a few days no line of distinction can be observed be- 

 tween them, the two being united into one individual, 

 and so continue to grow during the rest of their lives. 

 This union appears to be analogous to that of engraft- 

 ing in plants, only with respect to the young sponges it 

 is voluntary. 



17. After leaving the parent, these little animals float 

 about for a day or two, when finding a suitable place, they 

 fix themselves firmly to a stone or rock, and there gradu- 

 ally increase to the adult size, and in their turn send forth 

 their progeny as above described. 



18. These facts, of course, could only have been ascer- 

 tained by placing the parent-sponge in a vessel of sea- 

 water. Many of these observations were made in vessels 

 no larger than watch-crystals. 



POLYPIFERA. 



19. The term polypifera is the name of the order, 

 and means animals bearing polypi. The name polypus 



In what manner do they move through the water? What is said of 

 the union of two of these animals into one? What does this union ap- 

 pear to be analogous to? What becomes of the young sponges after 

 being detached from their parents? What is the meaning of the term 

 polypifera? 



