668 FRANK E. BEDDAED. 



Embedded in the thickness of the muscular coat is a dense 

 layer of tissue which stains darkly ; this layer is of some thick- 

 nessj but apparently homogeneous throughout ; here and there, 

 for instance, in that part of it which covers the egg-sac as 

 shown in fig. 12, favorable sections demonstrate that it is 

 a membrane, el; it is usually much bent, showing the zigzag 

 contour illustrated in the figure ; in all probability it is 

 of the nature of elastic tissue, and permits of the easy recovery 

 of the original dimensions of the sac after it has been unduly 

 distended with sperm. 



The lining epithelium of the sac is, as a rule, more than one 

 cell thick ; there appears usually to be an innermost layer of 

 fairly regular smallish cells ; here and there an extensive pro- 

 liferation of these has taken place. The whole character of 

 the cellular lining of the sac indicates that it is not formed as an 

 invagination of the epidermis ; nor, as will be seen later, is 

 it. It has been said that the anterior wall of the sac passes in 

 close relation with intersegmental septum 12 — 13. In 

 longitudinal sections — which are, I may remark, much more 

 useful for studying the structure of worms than trans- 

 verse sections — the anterior wall is seen to be not merely 

 in continuity with the septum ; it is formed by the 

 septum itself. 



Ovaries. — I could not find the least trace of these organs 

 in fully mature worms, either by dissection or in sections. 

 That the ovaries should be evanescent structures in an earth- 

 worm is rather unexpected. They are present in young stages, 

 where they exhibit the usual position and structure, though 

 like the testes they are much elongated and very narrow. 



Egg- sacs. — In a dissection the egg-sacs can hardly be dis- 

 tinguished from the great unpaired spermathecal sac in which 

 they lie ; a careful inspection shows that at the point where 

 the oviduct arises there is a slight bulging outwards of 

 the sac ; this has a browner coloration than the rest of 

 the walls of the sac. This, however, is no more conspicuous 

 than is represented in fig. 9, where the spermathecal sac 

 and the oviducts are displayed in a slightly diagrammatic form. 



