THE ANIMAL KINGDOM 



II 



the pharynx to a ventral subintestinal blood vessel. Smaller branches 

 distribute blood to the body-wall and intestine. External respiration 

 takes place through the skin. External filamentous gills sometimes occur 

 in forms with parapodia. The muscles, both of the body-wall and of the 

 alimentary canal, are divided into circular and longitudinal sets. 



The sexes, usually, are separate, and the gonads are limited to a few 

 segments of the body. Germ cells find their way to the exterior either 



A. QJMBRICUS. 



LATERAL ASPECT. 



SOMITES.-- 



OPENING OF 

 SPERM-DUCT. 



MUSCLES. 

 NEPHfiOSTOME 

 NEPHRIDIOPORE 



GIANT FIBER 



B EARTHWORM -CROSS SECTION 



SUBNEURAU BUOOD VESSEL 



Fig. 8. — Liimbricus, a type of the phylum Annelida. Figure A shows the com- 

 mon earthworm in left lateral aspect. (Redrawn after Vogt and Jung.) Figure B is 

 a cross section in the trunk region. (Redrawn after Chidester, Courtesy of D. Van 



Nostrand.) 



through pores in the body wall, or by way of ciUated tubules, the coelomo- 

 ducts. Many annelids undergo metamorphosis from a " trochophore " 

 larva. 



Four thousand species are known. 



Phylum 10. MOLLUSC A 



Molluscs are coelomate and non-metameric. The body consists 

 of mantle, mantle-cavity, and foot without paired appendages. The 

 mantle cavity receives digestive wastes and the products of the excretory 



