200 



ClELHELMIXTHES 



In de\-clopment die brachiopods recall both Sd^ilta and the Annelida. 

 Thev resemble 5.JC'"'' i" I'l-'t "^ Ar^^iopc the ca-lom arises by outgrowths from 

 the archenteron dig. jyob divided later by septa into three pairs of pouches. 

 They are annelid-Hke in the form of larva and in the presence of ckvta? which 

 are formed in separate follicles. Brachiopods were formerly so numerous that 

 they are among the most important fossils in the determination of geologic 

 horizons. Now there are but few species, some inhabitants of the greatest depths 

 of the sea. 



Fig. 270. — Development of brachiopod (after KowalevskyV .4, gastrula with 

 earlv enteroccelic pouches; B, closure of blastopore; t", ccelom separated, body annu- 

 lated; D, cephalic disc and mantle developiing, the latter with long sets; £, attached 

 embryo, the mantle lobes folded over cephalic disc (sct;e omittedb r, cephalic disc; 

 d, dorsal lobe of mantle; f, enteroccele; >ii, mantle; 'c, ventral mantle lobe. 



Order I. Ecardines. 



Hinge absent: valves similar, the stalk passing between them (Liiigtila*), 

 or unequal, the ventral perforated bv the stalk (Dis- 

 cina). or the animal is direcllv attached by the shell 

 tCrdllid). 



fttitriondlis.'^ 



llmge 

 forated 

 choinlla,'- 

 Spirifrr, Orlli 

 genera. 



Order II. Testicardines. 



present, \-alves unequal, the ventral per- 



bv the stalk, anus degenerate. Rlivn- 



Tcrrbraliiliiia'--' in our colder waters. 



Ptiitjiiicnis, .[Irvpj, important fossil 



Siunmary of Important Facts. 



(i) The CGELHELMINTHES have a well-developed body cavity (cadom). 



(2) The Ch.etoc.N'.vthi are hermaphroditic worms with three pairs of 

 cojlomic pouches, with hns, ard bristle-like jaws. 



(j) The Nem.\tod.\ are mostly dicecious, usually parasitic, elongate worms, 

 with cylindrical unsegmented body, with nerve ring (no ganglia"), paired excre- 

 tory organs, and tubular gonads. 



(4) The most important species parasitic in man are Ascaris Itiiiihricoidcs 

 in the small intestine, Owiiris vcDiinularis in the large intestine, Aiikylosloum 

 Jnodcnalis, and the notorious Trichina spiralis. In hot climates Filarij saii- 

 giiiiiis hoiiiinis and Dracuncnhis mcdiiicnsis. 



(5) The GoKDi.vcE.^ have mesenteries and splanchnic mesoderm; they 

 are parasitic in insects. 



