^^ ZOOGENESIS "^^^ 



type of animal as adults. They may develop directly from the 

 egg, or they may pass through one, two, or several larval forms. 



The most familiar exam^ples are the tapeworms, the hook- 

 worms, various "worms" affecting children, dogs, cats, cattle, 

 etc., the "vinegar-eels," the "wafers" of oysters, and the "hair- 

 snakes" seen wriggling in pools and troughs in summer, which 

 in the young stages are parasites in insects. (Figs. 5, p. 5; 54, 

 55, p. 97; 81-83, p. 161; 96-99, p. 175; ii6-i2.8, p. 185; 130, p. 103; 

 135, p. 103.) 



Ctenophora — sea-walnuts, the Venus' girdle, etc. — A fairly 

 large group found only in the sea, more especially in the warmer 

 waters. The ctenophores are nearly all free-swimming and are 

 most abundant below the surface zone, but occasionally appear 

 in great numbers at the surface. A few of them are elongated, 

 flattened and worm-like and creep about on objects on or growing 

 from the sea floor. Most of them are transparent and as clear as 

 glass, the vibratile plates showing a beautiful play of iridescent 

 colors. A few are more or less deeply colored, usually pink 

 or red. (Fig. GG, p. iii.) 



CcELENTERATA. — A Very large and very highly diversified group 

 including the sea-anemones or animal-flowers, the hydras, the 

 hydroids, the sea-pens, the sea-fans, the corals, the millepores, 

 the gorgonians, the antipatharians, the alcyonarians, the jelly- 

 fishes, the ctenophores, and various other types. Most of the 

 coslenterates are marine, living in shallow water or in water of 

 moderate depth, but mxany are found in very deep water and a few 

 in fresh water, the best known of these last being the hydras and 

 the little fresh water jellyfishes which are so curiously erratic 

 in their occurrence. Many coelenterates are solitary, like the 

 hydras and the sea-anemones, but most of them form bush-like, 

 tree-like, wand-like, fan-like, mushroom-like, feather-like, en- 

 crusting, or solid and massive colonies. Many form semi- 

 transparent or beautifully and delicately colored free-floating 

 colonies, of which the Portuguese man-of-war is an example. 

 Some kinds are only found in association with other animals, 

 particularly crabs (fig. 17, p. 47) and annelids, while a few are 

 parasitic on other coelenterates, on fish-eggs, ttc. (Figs. 3, 4, 



P- 55 69-73» P- 1^7; 75-So» P- 1435 io3» i^S' io7» P- i75' no" 

 119, p. 185.) 



PoRiFERA — Sponges. — A large and much diversified group with 



[l6j ^ 



