328 



COELHELMINTHES. 



Now tliere are but few species, some inhabitants of the greatest depths of 

 the sea. 



Fig. 301.— Development of brachioporl. (After Kowalevsky.) J.gastrula with early 

 enterocfjelic jiouches; _B, closure of blastopore; C, cfjelom separated, body annu- 

 lated; J>, cephalic disc and mantle developing, the latter with long setip; K, at- 

 tached embryo, the mantle lobes folded over cephalic disc (setee omitted), c, 

 cephalic disc; d, dorsal lobe of mantle; e, enteroccele; »*), mantle; \\ ventrol man- 

 tle lobe. 



Order I. Ecardines. 



Hinge absent.; valves similar when the stalk passes out between them 

 ilAngnla *), or unequal when the ventral is perfo- 

 rated by the stalk ( Disci/ia) or when the animal is 

 directly attached by the shell (Crania). 

 Order II. Testicardines. 

 Hinge present, valves unequal, the ventral 

 perforated by the .stalk; anus degenerate. Rhyn- 

 choiiella* Terehrattdina* in our colder waters. 



liG M-Tnchratunnam:>- ^P'"f''''' Orthw, Pentameru.% 4?r)/;i«, important 

 teiitiionalis* fossil genera. 



Summary of Important Facts. 



(1) Tlie CfELHELMINTIlES are cliaractcrized by a well-developed body 

 cavity (eceloni). 



(3) The Ch.etognathi are hermaphroditic worms with three pairs of 

 coelemic pouches, witli fins, and bristle-like jaws. 



(3) The Nbmatoda are mostly diwcious, usually para.sitio elongate 

 worms, with cylindrical unscgraented body, with nerve ring (no ganglia', 

 paired excretory organs, and tnlnilar gonads. 



(4) The most important sjiecies parasitic in man are Asearis hniibri- 

 coidts in the small intestine, Oxijnri.s ivrtnii:u!aris in the large intestine, 

 the blood-sucking Ankylostoma diinilerialis, and the notorious Trichina 

 spiralis. In hot climates occur Filaria sanguinis Jioiiiinis and Dracun- 

 cnlns medinensis. 



(5) The GoRDiACF.A have mesenteries and splanchnic mesoderm; they 

 are parasitic in insects. 



(6) The AcANTHOCEPHALi lack alimentary tract, have a spiny proboscis 

 and a very complicated reproductive apparatus. The adults are parasitic 

 in vertebrates, the young in artliropods. 



