42 



FIRST LESSONS IN ZOOLOGY. 



(Fig. 56). It secretes a yiscid fluid lining its hole, up 

 whicli it moves, pushing itself along by its bristles. At 



night it leaves its hole, 

 swimming on the surface 

 of the water.* 



The body consists of from 

 one hundred to two hun- 

 dred segments. The head 

 consists of two segments, 

 the first with four eyes and 

 two pairs of tentacles. Tlie 

 second segment bears four 

 tentacles. Each of the other 

 segments bears a pair of pad- 

 dle - like ap- 

 pendages, which may be best studied by exam- 

 ining one of the middle segments (Fig. 40). 

 Some sea- worms are beautifully phosphores- 

 cent. The young of all sea-worms (Fig. 43) 

 are ciliated, and swim on the surface of the' 

 Thus, young or larval worms differ en- 



Fio. 41 A, Head of worm, with the 



proboscis (pharynx) protruded ; B, the 

 same retracted; «, mouth; d, pharyn- 

 geal teeth; 6, stomach; ega, pliarynx; 

 geh, muscles for everting the pharynx; 

 df, for retracting it. 



sea. 



Fig. 42.— Ciliatea 

 larva of a sea- 

 worm. 



tirely from their parents in shape, size, and 

 habits, leading different lives, and exposed to greater dan- 

 ger than the full-grown animals. 



Classes of Vermes (Worms). 



1. Body flat, no body-cavity PlSiyhelmintUes (Plat worms). 



3. Body round, witli a body -cavity. . . Nematelminthes (Round worms). 



3. Bo'dy microscopic, moving by two 



ciliated flaps Rotatoria (Wheel animalcules). 



4. Body minute, in a solid cell Polyzoa (Moss animals). 



5. Two shells, upper and lower, at- 



tached by stalk, with two arms. Brachiopoda (Shelled worms). 



6. Body jointed, usually with feelers, 



eyes, bristles, oars, and gills. .Annnlata (Earth-worms, Sea- 

 worms). 



* See Verrill's works in U. S. Fish Commission Reports, etc. — Ver- 

 rill and Smith's Report upon the Invertebrate Animals of Vineyard 

 Sound, 1874. — Also Trumbull: Anatomy and Habits of Nereis virens 

 (Transactions Connecticut Academy, iii, 1876, 265-280); Sedgwick 

 and WUson : Biology (Chapters 7-10); and Whitman : External 

 Morphology of the Leech (Proc. Amer. Acad. Arts and Sc, 1884). 



