THE ANATOMY OF SUTROA. 199 



The probability that these sacs are coelomic spaces, and not glandular structures at 

 all, is rendered very great by the fact that on one side of the body a single diverticulum 

 of the spermatotheca lay within the sac. # 



The cvaries are figured by Eisen as occurring in the XXXIInd segment. The true 

 ovaries, however, lie in a more normal position ; I found them in segment XI, cor- 

 responding exactly in position to the testes. They appear to be attached not only to the 

 septum of that segment, but also to the cells of the vas deferens funnel. It is true that 

 these supposed ovaries contained no ripe ova, so that I cannot be absolutely certain 

 about the identification. Ripe ova occurred in two of the posterior segments enclosed 

 within the sperm-sacs. The ova, as in all the aquatic genera, are very large, and are filled 

 with spherical yolk corpuscles. 



The oviducts open on to the intersegmental groove XI-XII. In sections through 

 the organ a deep cleft is seen to separate the oviduct anteriorly into two halves. 

 In this has collected a quantity of debris, evidently on its way to the exterior. 



The single median spermatotheca is, as will be gathered from an inspection of 

 Eisen's figure (loc. cit., PL xiv. fig. 7), very remarkable in shape. It consists of a large 

 median pouch, from which arise a number of narrow tubular diverticula. Of the 

 homologies of the organ, Eisen writes as follows : — " Considering this central spermatheca 

 in Sutroa in connection with the two spermathecse in JRhynchehnis, two theories are 

 admissible. One is, that in Sutroa one of the spermathecae has failed to develop, and 

 that the remaining one has become central by being moved towards the central ganglion, 

 which latter it considerably displaces. The other theory is, that in Sutroa the two 

 spermathecae are represented by, or homologous with, the pairs of branched spermathecal 

 sacs opening into the spermathecal atrium. The latter, then, is only an unfolding of the 

 body-wall deep enough to cause the spermathecae to become merely appendices to the 

 central spermathecal sac or atrium. I believe this latter theory to be the correct one." 

 It seems to me that there is no need for the existence of a " spermathecal atrium." 

 What has happened is, that there has been a fusion between the originally paired sacs, 

 resulting in a single median sac ; in Cryptodrilus unicus we have another example of a 

 similar fusion of the spermatothecse in the middle line. The spermatotheca (see fig. 5) is 

 divided into two parts ; distally it is a large, comparatively thin walled sac ; the proximal 

 part is a duct, with more muscular walls, opening on to the exterior. At the junction of 

 the two are given off the diverticula. The existence of diverticula in an aquatic genus is 

 a remarkable fact, particularly in the Lumbriculidse. They agree, moreover, with the 

 diverticula of earthworms in being of a different structure from the main pouch. The 

 epithelium is lower and more darkly staining ; the muscular walls are thicker. Further- 

 more, the diverticula contain nearly all the sperm. This, again, is a point in which they 

 resemble the diverticula of earthworms. Eisen mentions that he found in one instance 

 " an interior porus in the free end of the spermatheca similar to the one described by 



Compare the enclosure of the spermatotheca of Hrjperiodrilus and Heliodrilus within a ccelomic sac (Quart. Joum. 

 Micr. Sci., vol. xxxii. p. 235). 



