Water 



37 



In air the body surface is kept moist by excreted water, and upon irritation 

 coelomic fluid is lost through the dorsal pores. A Japanese worm is said to 

 throw coelomic fluid a distance of one foot into tfie air. •''' Fluid loss by way 

 of the intestine is slight. Fluid collected from the anterior end of the intestine 

 has a higher osmotic concentration than the blood. "■' Worms tied at both 

 ends gain weight in water no faster than worms not tied. Pressure of 4.5 cm. 

 I LO measured by a cannula in the gut corresponds to an intestinal e.x'cretion 

 of 0.25 per cent of the basal weight per hour. -■'••* 



Nephridial excretion by worms in water is 2-2.5 per cent of the basal weight 

 per hour.^' ^''' -''•'■ Analysis of earthworm urine, collected by an ingenious 

 device, is shown in Table 1. The urine is hypotonic to blood and coelomic 



TABLE 1. COMPOSITION OF BODY FLUIDS OF PHERETIMA POSTHUMA* 



*From Bahl. ''■ '" See also Table 9 in Chapter 3. 



fluid and contains much less salts but more urea. In Lituihricus terrcstris in 

 tap water the chloride concentration in urine is 20 mg. 100 cc. and that in 

 coelomic fluid is 270 mg./lOO cc. The osmotic concentration of coelomic fluid 

 is equivalent to 0.53 per cent NaCl and that of blood is slightly lower. -*'""' 



Earthworms show a wide variety of types of nephridia (reviewed by BahP^). 

 Some are large, occurring as one pair per segment; others are small and very 

 numerous in each segment. The best known nephridia open into the coelom 

 by a funnel, but there are many which are closed interrially. Some earthworms 

 (e.g., Pherethna posthwna in India) have some nephridia which empty into 

 the intestine, i.e., are enteronephric; whereas others (e.g. Lwuhricns, Euty- 

 phoeus') have all of the nephridia opening externally, i.e., are e-xonephric.'"* 

 The castings of enteronephric worms are drier and these worms live in a drier 

 environment than exonephric worms. 



Coelomic fluid enters the nephridial funnels (nephrostomes) under the force 

 of ciliary beat; particles such as Chinese ink are seen to enter the nephridia 

 from the coelom only when the distal portion or bladder is empty. ■'*'' Dyes 

 and particulate matter may be found inside nephridial epithelial cells; these 

 substances are either absorbed from the tubule'''*' -''' or are phagocytized by 

 migratory chloragogue cells and deposited in the tubules. Breakdown products 

 of hemoglobin are transferred from blood to certain nephridial cells where 

 they are stored. ^'^ Fluid collected in the ampulla and bladder is markedly 

 hypotonic to the coelomic fluid, hence capacity to form hypotonic urine is 

 greatest in the wide tube of the ampulla. -'^•'^" Ciliary propulsion, active trans- 

 port across the tubule cells, and phagocytosis combine to produce the urine 

 from coelomic fluid and blood. Cytological comparison of nephridia from 

 worms in water and in air might provide evidence regarding secretory function. 



