32 



BRANCH YERMKS, 



provided with three small lance-like teeth, which readily 

 puncture the patient's skin, causing a painless flow of 

 PIG 43 blood. During the warmer months, they 



o crawl from the water and deposit their 



eggs in the moist mud. These in a few 

 days hatch, the young at once seeking 

 the water. Several allied forms inhabit 

 our fresh-water ponds and streams. 



\ v 



We now come to a few worm-like 

 animals, the precise relations of which 

 are not settled. The Polyzoa (poi I zo'a), 

 and Brachiopods (brak'i o podz), though 

 generally classified with the Avorms, 

 present affinities with higher forms, 

 and are regarded by some naturalists 

 as belonging to a separate Branch, the 

 MOLLUSCOIDEA (mol lus koi'de a). 



The Polyzoa, though found in fresh- 

 water, abound in the ocean, where their 

 small calcareous, or horny, capsules 

 form incrustations over nearly every 

 submerged object. These capsules, each 

 of which contains a Polyzoon quite dis- 

 tinct from the others, are often ar- 

 ranged in a branching form, giving the 

 colonies a strong, though superficial, re- 

 semblance to the branching Hydroids. 

 Through the thin wall of the capsule, the structure 

 of the animal can often be determined. The mouth, 

 surrounded by a number of ciliated tentacles, opens into 







an elongated and complete alimentary tract, through the 



Hi r~(' do me die i n'i'lis. 



Medicinal Leech, showing 

 chief points in its anat- 

 omy. 0, Mouth. <S', Stom- 

 ach. C, Cerebral ganglion 

 uniting with the ventral 

 chain of ganglia, F, 

 through the cesophageal 

 ring. T, Terminal suck- 

 er. A, View of mouth, 

 showing the three lance- 

 like "teeth." 



