3470 



CCELENTERA TES 



settle down. Lucernaria has been found as deep as three thousand three hundred 

 feet, but appears to prefer to settle in shallower water. The nearest relations of 

 Lucernaria are the Tesseridcz. These creatures are small and swim about freely, 

 having an elegant long bell-like shape. The edge of the disc is drawn out into 

 alternately longer and shorter arms, eight to sixteen in number. 



SEA ANEMONES AND CORAI^S Class Anthozoa 



We turn from the free-swimming Scyphomedusse to the permanently fixed 

 polyp forms, namely, the sea anemones and corals; the latter of which leave 

 behind them monuments compared with which the pyramids sink into insignifi- 

 cance. Wherever these often minute animals settle, they build up great masses of 

 rock which may form part of the solid ground of the globe. Although Aristotle 



and his contemporaries recognized the sea 

 anemones as animals, almost two thousand 

 years elapsed before corals were considered to 

 be related to them. In describing the develop- 

 ment of a small coral discovered on the Arabian 

 coast, and named Monoxenia darwini, Haeckel 

 states that the polyp, which is one-eighth of 

 an inch long, is of strictly radiate structure, the 

 mouth, which lies at the upper end of the 

 cylindrical body, being surrounded by eight 

 feathered tentacles. It is attached to some 

 substratum by means of a flexible disc at the 

 opposite end of the body to the mouth. It is 

 clear that it has no hard skeleton, as the 

 shape of its surface is changeable; and its 

 internal structure must be shown by transverse 

 and longitudinal sections. The development 

 of Monoxenia commences with the egg re- 

 peatedly dividing into many parts (C, D, E}. 

 This process, which is common throughout the 

 animal kingdom and is called egg segmenta- 

 tion, in this case proceeds so simply and 

 regularly that it ends in the production of a 

 hollow sphere inclosed by a single layer of 

 cells (G). Each cell sends out a long cilia or 

 whip-like process (F) by means of which the 

 larva turns about and swims in the body fluid 

 of the parent polyp. One-half of the sphere 

 now becomes infolded into the other half (If) , 

 and forms what is called a gastrula (/, PC) . The 

 term gastrula has taken a great place in zoology 

 in recent years, since the Russian naturalist, 



Monoxenia darwini. 

 (Highly magnified.) 



