CONTEIBUTIONS TO THE ANATOMY OF THE HIEUDINEA. 475 



When empty of blood they shrink in virtue of a slight 

 muscular development in their walls to a very small size, but 

 when fully distended each presents a diameter of perhaps a 

 quarter the breadth of the body. They are about twice as long 

 as broad and each presents a constriction in the centre, being 

 divisable into an anterior and a posterior portion of nearly equal 

 size. Within these are lodged the funnels of the nephridia, 

 (figs. 51 and 62). 



They have been long known in Nephelis, having been first 

 described by Johannes Miiller under the name of Lungen- 

 gefassen, but although functionally they are perinephros- 

 tomial yet they differ morphologically from the perinephros- 

 tomial sinuses of other Hirudinea. And I think it would be 

 well to insist upon their histological significance by terming 

 them botryoidal sinuses. 



They have been described by Von Siebold^ and Leydig,^ but 

 more recently and fully by Bidder/ the latter observer showing 

 that they contained the nephridial funnels which were dis- 

 covered by Von Siebold. 



In Nephelis they are mere enlargements of the lumen of 

 the botryoidal tissue in the neighbourhood, this latter forming a 

 dense mass around them, a very slight muscular develop- 

 ment occurring in connection with their walls and serving to 

 empty their contents. 



In Trocheta, actually bounding the lumen, there is a single 

 layer of cells containing pigment granules, and presenting a 

 slightly ragged inner surface ; these are clearly cells similar to 

 those forming botryoidal vessels (fig. 51, ep.). A definite 

 muscular wall obtains, the muscle-fibres themselves being 

 very small; outside this there is a considerable amount of 

 ordinary ectoplastic connective tissue. 



The lumen is thus not continuous on all sides with that of the 

 botryoidal tissue around it as in Nephelis, but there is a de- 

 finite vessel opening into the sinus (fig. 51, t) which has the 



' ' Lebrbuch der vergl. Anat.,' p. 216. 



2 ' Bericbte voa der Koaig. zootom. Anstalt zu Wurzburg,' 1849, p. 14. 



' ' Untersucb. einiger Hirudineen,' Dorpat, 1868. 



