404 HIRUDINEA 



purely mesoblastic structures, not except perhaps the very 

 extremity derived from an ingrowth from the epidermis. "We 

 have, however, other Oligochaeta in which there are closer 

 resemblances to what has just been described in the Hirudinea. 

 In more than one point the aberrant family of the Eudrilidae 

 come nearer to the Hirudinea than any other Oligochaeta, in 

 spite of Brancliidbdella with its jaws and sucker. Now in 

 Eudrilus the ovary is enclosed in a capsule which becomes con- 

 tinuous with the duct of the great sperm-holding pouch, itself an 

 invagination from the exterior; there is no reason in this 

 Annelid why the ova should not reach the exterior by this 

 system of ducts, although there is no actual experimental proof 

 that they do so. In any case there is also an oviduct correspond- 

 ing to that of Lumbricus, which opens into the opposite side of 

 the duct of the spermathecal pouch on the one hand, and into 

 the receptaculum ovorum on the other ; it has no direct con- 

 nexion whatever with the sac containing the ovary. If we were 

 to cut off the receptaculum and the oviduct and reduce the sper- 

 mathecal sac to its duct, the result would be much the same as 

 we find it in the leech. 



Cocoon. The practice of forming a cocoon for the shelter of 

 the eggs and of the developing young is shared with the Oligo- 

 chaeta ; but not all leeches deposit their eggs in this manner. 

 Glossiplionia, for instance, carries its eggs upon the ventral face of 

 the body, where the young remain for some time after they are 

 hatched attached by the posterior sucker to their parent's body, 

 and from which situation of safety they make short excursions. 

 Other leeches deposit their eggs singly, but agglutinated to- 

 gether upon stones, etc. In the medicinal leech the cocoon is 

 ovoid in shape, and from the end, which is closed by a temporary 

 plug, the young when ready escape. This cocoon is deposited, as 

 is that of an earth werm, in soil near to the borders of a marsh 

 or pond, so that the young, while enjoying the requisite degree 

 of moisture, may not be injured by a too wet environment. On 

 the other hand PontoMella and some other leeches lay their 

 cocoons attached to bodies actually submerged in the water. 

 The cocoon is secreted, as in Oligochaeta, by the clitellum, and 

 as in them, is drawn off over the head, the ova and sperm pro- 

 bably flowing into it during the process. The elasticity of the 

 slightly hardened mucus causes the two ends of the cocoon to 



