126 



PRINCIPLES OF ANIMAL BIOLOGY 



of protonephridia, which are fine tubes rising in flame cells and discharg- 

 ing to the exterior. A portion of such a system is sliown in Fig. 90, 

 and the structure of a flame cell in Fig. 91. The flame cell is somewhat 

 stellate or irregular in shape, hollowed out to form a funnel-shaped cavity 

 within itself. A number of long slender ciha (the "flame") take their 

 origin from the body of the cell and hang freely into the fnnn(>l-shaped 

 cavity. In life the cilia beat continuously and by their beating cause 

 currents in the liquid which is excreted into the funnel by the cell. 



Nephridia. — In the annelid worms each segment or somite (with some 

 exceptions) is provided with a pair of more or less coiled tubes, the ne- 

 phridia, which have a funnel-shaped 

 ciUated opening, the nephrostomey 

 which projects through the septum 

 into the cavity of the somite ahead. 



Fig. 92. — Nephridium of earthworm, 

 schematic, neph, nephrostome; ac, por- 

 tion of septum; 1-6, portions of tubule of 

 the nephridium; 7, opening to exterior. 

 {From Hesse and Doflein after Maziarski.) 



Fig. 9.3. — Structures from vertebrate kidney, 

 diagrammatic. A, Malpighian corpuscle; B 

 and C, cross-sections of uriniferous tubules at 

 different levels; ay, afferent vessel; he, Bowman's 

 capsule; cap, capillary; «Z, cilia; ev, efferent 

 vessel; gl, glomerulus; ut, uriniferous tubule. 



There it opens directly into the body cavity or coelom. The other end 

 of the coiled tube is connected to the body wall where it has an opening 

 to the exterior. The body of the nephridium in the earthworm, shown dia- 

 grammatically in Fig. 92, is composed of coiled tubes arranged in three 

 distinct loops. The nephrostome sweeps in liquid and small solid particles 

 by the action of its cilia. A portion of the tube is also provided with cilia 

 which assist in propelling hquids through the nephridium to the exterior. 

 Other portions of the nephridium are composed of cells which have a 

 secretory function. 



Kidneys. — The excretory organs of vertebrate animals consist of 

 large compact glands, the kidneys, which are made up of convoluted 



