552 MONTGOMERY— MORPHOLOGY OF THE [Apiil 24, 



Biirger suggests they may either be secondary invaginations of the 

 epidermis, " or the nephridium itself must break a new way through 

 the body wall. Judging from the adult animal the first alternative 

 must be the case." 



4. Gastrotricha. * 



There is a single pair of much convoluted tubules, lateral from 

 the intestine, opening near each other on the ventral surface with- 

 out ex<:retory vesicles. Each ends internally with a single closed 

 bulb, but it is not determined whether it contains a single flagellum 

 or a row of cilia (Zelinka, 1889). 



5. Rotatoria. 



The excretory organs have been most carefully described for 

 the Philodinids (Zelinka, 1886. 1888, 1891, Plate, 1889), Floscu- 

 lariidse (Montgomery, 1903, Gast, 1900), Melicertidse (Hlava, 1904, 

 1905), Atrochidse (Wierzejski, 1893) and Asplanchnidss (Hudson 

 and Gosse, 1886, Rousselet, 1891, Weber, 1898). There is always 

 a right and left main canal ; the flame cells may be directly attached 

 to these (most Philodinidse), but more usually are placed at the 

 ends of capillaries, branches of a main capillary that open into the 

 main canal at one or two points. The number of flame cells on 

 eash side of the body is small, usually from three to six, and in 

 that case they are relatively large; but in the Asplanchnidae there 

 are some fifty of them on each side sessile on a main capillary. 

 Their great number here may be due to the large size of these 

 species. The main canals unite posteriorly into a short unpaired 

 duct that opens into the cloaca ; and anteriorly they are usually con- 

 nected by a transverse commissure (absent in some Philodinidse). 

 The main canals have an intracellular cavity, are composed of a 

 few cells and are usually without cilia ; terminal flame and capillary 

 is a single cell, the termination of which is entirely closed from the 

 body cavity and contains an internal flame of cilia and (in As- 

 planchna) has a couple of long flagella on the outer surface. 



The early development of these structures has not been de- 

 termined (Zelinka, 1891). 



