SOME POINTS IN THE ANATOMY OP POLYCH.ETA. 255 



above the intestine, and its external opening is a little ventral 

 to the origin of the first branchia. Between the nephridial 

 opening and the root of the branchia is the aperture of a 

 peculiar glandular organ whose function we have been unable 

 to ascertain. On dissection of a fresh specimen this gland is 

 seen as a milk-white, opaque, cylindrical body about one eighth 

 of an inch long, free everywhere except where it is continuous 

 with the body wall round its opening to the exterior. The 

 efferent duct of this gland is lined by a high columnar epithe- 

 lium, of which the component cells are solid and columnar; 

 throughout the rest of the gland there is a layer of long solid 

 nucleated cells next to the basement membrane, but these are 

 covered by other layers of large vacuolated cells whose walls 

 form a network nearly obliterating the lumen of the organ. 

 The wall of the gland is well supplied with pseudhsemal vessels. 

 The third somite (i. e. second branchiferous) and the fourth 

 are unprovided with nephridia, but the latter contains a 

 nephrostome belonging to the nephridium of the fifth somite ; 

 the sixth somite is likewise provided with a nephridium whose 

 nephrostome is in the fifth somite. The nephrostomata are 

 simple elongated funnels with their apertures directed for- 

 wards ; they are not provided with such a series of digitate 

 processes as is seen in Lanice and Arenicola. The gonads are 

 of the usual type, masses of undifferentiated cells attached to 

 the exterior of the nephrostomata on the mediad side. The 

 reproductive cells become detached at a very early stage and 

 pass through the rest of their development in a free condition 

 in the coelom. It is certain that the spermatozoa reach the 

 exterior by passing through the nephridia ; in a series of 

 sections of a ripe male I saw the nephrostomata and nephridial 

 tubes distended with them. Between the two posterior 

 nephrostomata and the body wall pass membranes, which are 

 rudiments of transverse septa. There is also a rudiment of a 

 septum between the second and third somites (first and second 

 branchiferous). The external apertures of the two posterior 

 nephridia are ventral and posterior to the notopodial setae of 

 their somites. 



