CONTRIBUTIONS TO THE ANATOMY OF THE HIRUDINEA. 477 



remain in different remnants in different genera. No better 

 instance can be given of this than the varying position of the 

 nephridial funnel in Clepsine, Pontobdella and Hirudo. 



The lumen of existing coelom as above described comes into 

 communication with the lumen of a true vascular system which 

 was probably derived at a very early period from the archaic 

 enterocoele. That such communication is of a secondary nature 

 and not a persistence of the original communication, which 

 must have existed if one developed from the other, is indicated 

 by the existence of the colourless amoeboid cells in the ovarian 

 sac, and around the vas deferens in Hirudo. These were pro- 

 bably closed at a very early period before the development of 

 haemoglobin. This may have a phylogenetic bearing only, but 

 it may be, and I should think very possibly is, a process which 

 is repeated ontogenetically. 



The communication between existing ccelom and the true 

 vascular system occurs in one of two ways : 



1. Vessels may terminate with an open mouth, which is 

 apparently provided with a sphincter in certain portions of the 

 coelom, e.g. the lateral dilatations and branchiie. 



2. Vessels (capillaries only, probably) may acquire a con- 

 nection with new sp 3 (botryoidal, &c., tissue), which are 

 forming in the connective tissue, these communicating on the 

 other hand with small coelomic remnants. 



The former of these ways is characteristic of the Rhynco- 

 bdellidse, the latter of the Gnathobdellidse. 



This development of new coelomic space (botryoidal tissue) 

 may be termed metacoelosis. 



This new space in its highest development encloses the 

 nephridial funnel (Nephelis), and the perinephrostomatous 

 portions of it may acquire a definite musculature, and the 

 " botryoidal " cells become modified, so as to form a secondary 

 coelomic epithelium, as in Troche t a. 



An archaic enterocoele thus gradually undergoes diacoelosis, 

 being replaced by a metacoele. This primary and secondary 

 coelom occur simultaneously side by side in all existing Gna- 

 thobdellidse. In the Rhyncobdellidse considerably more of the 



