SOME RECENT MEMOIRS UPON OLIGOCHMTA. 199 



which varies in different genera, and of which it would be 

 impossible to give any detailed account without the assis- 

 tance of figures. There is a separate receptaculum ovorum 

 like that of the common earthworm, with which is connected 

 the oviduct. This system of sacs, through which the ova 

 can travel in so far as there are no physical hindrances, also 

 contain sperm, and play the part of spermatheca? or a sperma- 

 theca. They commonly open by a single ventral pore ; 

 sometimes the structures are paired as in the genus Eudrilus 

 itself. Now these pouches generally contain sperm, and 

 there is therefore the possibility of the ova being impreg- 

 nated within them ; Michaelsen has even suggested that 

 some species are viviparous. In a few genera, for example 

 in Heliodrilus, these pouches do not communicate with the 

 exterior except through the oviducts. They appear to do 

 so by a large ventral pore, but when careful sections are 

 made it is found that this pore is the mouth of a closed sac, 

 exactly like a spermatheca, which is enclosed within the 

 large pouch. Thus the ccelomic nature of this system of 

 sacs is established on anatomical grounds, and develop- 

 mentally they have been shown, at least in one genus, to 

 be derivatives of the intersegmental septa just as are the 

 sperm sacs of other earthworms ; their cavities are therefore 

 separated portions of the general ccelom. But, as already 

 mentioned, in most cases they do open on to the exterior 

 directly by a conspicuous orifice, and contain sperm which 

 probably finds its way into them by this orifice. The fact 

 that in some cases these sacs contain structures which are 

 precisely like the spermathecae of other earthworms, and 

 that in other cases where they open directly on to the 

 exterior the character of the lining epithelium changes near 

 to the orifice, becoming distinctly columnar, suggests that 

 we have to do here with the substitution of sacs derived 

 Irom the septa for the true spermathecae which are gradually 

 disappearing, only the extremity being left in the majority 

 ot cases. The second point with which I wish to deal 

 concerns the calciferous glands. Most, but by no means 

 all, earthworms possess one or more pairs of these organs, 

 which are attached to and open into the cesophagus. What- 



