243 Prof. M'liitosh'd Notes from the 



for the transmission of the reproductive elements, and 

 possibly also for an interchange l)et\vcen the coelomic cavity 

 and the exterior as in certain 01igo{'ha?ts, True ncphridia, 

 at any rate, are absent in Otrenin. "Whatever the fnnction of 

 these canals may be, Arnold AVatsou has shown that sperms 

 and ova esca|)C by dillerent channels. 



In front of the tail the liypodermic coating of the surface 

 is of moderate thickness. The massive muscnhir investment 

 is conspicuous, and it is difficult to distinguish where the 

 dorsal loniiitudinal muscle ends and the ventral begins, 

 though a fold above the miu^ous gland seems to indicate the 

 separation. '^I'he nerve-cords have shrunk to a small lenti- 

 cular area, which in minute structure has the same fibrillar 

 and granular character as in front. The intestine, held in 

 position by a dorsal and a ventral mesentery, is considerably 

 less, but it has large vessels or sinuses on each side, the 

 ampulhe from the ventral vessel passing into the large gonad 

 below the gut. Two mucous glands are still in evidence 

 under the dorsal M'all, and they have the same character as 

 in front. Moreover, their ducts open above the long line 

 of hooks in the space between these and the bristle-tuft, 

 which is now dorsal in position, and so leave the entire 

 lateral wall to the hooks ; thus the restricted area occupied 

 by the dorsal longitudinal muscles is defined. The whole 

 lateral and ventral regions are covered by the ventral longi- 

 tudinal muscles, Mhich, however, are much thinner than the 

 dorsal, the reverse of the condition in front. The con- 

 spicuous development of the gonads in this region and the 

 ampullte of the veunal vessel are noteworthy. The mucous 

 glands have now ceased (PL IX. fig. 14). 



One of the interesting features toward the tail is the 

 occurrence of the septa (PI. IX. fig. 15). Their first appear- 

 ance is indicated by the envelopment of the intestine and 

 its blood-sinuses by a sheath which springs from each side 

 of the vertical mesentery under the dorsal blood-vessel, and 

 stretches to the mid-ventral mesentery considerably below 

 the ventral blood-vessel. In such a view it might be sup- 

 posed tiiat the middle of the septum has been sliced, leaving 

 the upper and lower attachments ; but such will not explain 

 all the outlines of these posterior septa. 



Reproductive elements occur in the spaces outside the 

 septum as well as within it and its areas. Then the upper 

 and lower arches separate, each having a zigzag outline as 

 it passes to the body-wall. The coelom is thus divided into 

 six areas — two dorsal, two ventral, and the lateral with the 

 gonads inferiorly on each side of the gut. 



