iS94. EARTHWORMS AND THEIR ALLIES. 51 



about these sacs is that we have a series of stages in the substitution 

 of them for the true spermathecae. In several genera of Eudrilidae, 

 e.g., Heliodvilus, there is a single median spermatheca, apparently 

 definitely corresponding to the true spermathecae of other worms. 

 This is wrapped in a sac which also communicates with the ovary by 

 narrower passages. In Hyperiodrihis, the true spermatheca — in this 

 case as in the last quite independent of the envolving sac — is greatly 

 reduced in size. Finally, we have in the majority of Eudrilidae no 

 true spermatheca at all, unless the sac of mesoblastic origin opens on 

 to the exterior by means of its exceedingly reduced representative. 

 It seems clearly a case of the replacement of one organ by another 

 physiologically similar, but morphologically distinct. The spermathecae 

 are the organs which receive the sperm during congress. It is, there- 

 fore, a most inexplicable fact that occasionally they open not only on 

 to the exterior, but into the lumen of the gut. The fact was discovered 

 a good many years ago in the Enchytraeidae, where it often occurs, 

 by Michaelsen. I have found that in the North American genus 

 Siitroa, first described by Eisen, exactly the same state of affairs 

 unexpectedl}' exists. These facts may be commended to those who 

 are still arduously labouring in the hope of finding gill-slits in some 

 creature which is not a Chordate. The singular relationship betv.'een 

 organs which would appear to have nothing in common, is enhanced in 

 singularity by the fact that in an Eudrilid, Paradnlns, where the 

 spermathecae are of the mesoblastic type, precisely the same inter- 

 communication is met with. 



So much detailed research has been carried on of late by Benham, 

 Horst, Rosa, Michaelsen, Eisen, myself, and others, that it is hard to 

 compress into the limits of a short review like the present the results 

 obtained. I confine myself, therefore, to such as are of a wider 

 interest than to speciahsts. The last matter that I shall deal with, 

 omitting a vast amount of rather less important though highly in- 

 teresting work, is a curious case of change of function exhibited in 

 the family Eudrilidae, to which I have so often had occasion to refer. 

 In this family, as in others, there are calciferous glands appended to 

 the cEsophagus, which secrete carbonate of lime. In Michaelsen's 

 genus Stuhlmannia, and a good many of its more immediate allies, these 

 glands are metamorphosed somewhat. They still open into the gut, 

 but the lumen is greatly reduced, and does not by any manner of 

 means extend through the entire gland. The gland is, in the main, 

 solid, being built up of densely-associated cells, looking like peritoneal 

 cells ; the whole mass is permeated by a rich network of blood-vessels, 

 as in the typical calciferous glands. Here and there, however, the 

 cells in question have assumed the appearance of columnar gland 

 cells ; and when this modification has occurred, it is the invariable 

 rule that what looks like the lumen of a tubular gland is occupied by 

 blood. If there were not this singular change, one might be inclined 

 merely to com.ment upon the fact that the glands, instead of being 



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