EMBllVOLOGY OF CLEPSINE. 287 



account of the connection existing between the lateral and the 

 median sinus. In one important respect Lejdig's statements 

 cannot be accepted — namely, that the dorsal trunk stands in 

 free and open communication posteriorly wfth the median sinus. 

 This error which was not corrected by Bidder, has been accepted 

 by most authors and has found its way into our best text-books. 

 Leydig (109) claims to have found the same free communication 

 between dorsal trunk and median sinus in Piscicola. Here he 

 describes six pairs of loops at the posterior end of the ventral 

 trunk, each of which begins and ends at nearly the same point 

 of the same vessel ! Bidder (-^) did not find the ventral vessel, 

 and of course could not determine how the dorsal vessel ended. 



My own observations are confined to Clepsine marginata. 

 Specimens from 10 — 15 days old have been found the most 

 favorable for study. The entire circulatory apparatus is at this 

 time fully formed, and the pigment has not developed to such an 

 extent as to render it very difficult to trace the main channels 

 and branches with a low magnifying power. 



I have found the ordinary Uve box an indispensable instrument 

 in this part of my work. The pressure applied was generally 

 sufficient to check the flow of the blood, but not to stop the 

 pulsation. The entire circulation, I hardly need to say, cannot 

 be determined by the examination of a single animal. For 

 tracing difierent parts, different degrees of pressure are necessary, 

 and the best views of some parts are only seen when the pressure 

 is so severe as to result in the almost immediate death of the 

 worm. It is only after one has succeeded in tracing all the 

 parts individually that one, in rare cases, is able to follow all in 

 one individual. A constant supply of fresh material is of course 

 indispensable to success in such a study. To this end eggs were 

 collected in different stages, and by the time older specimens 

 were exhausted, new ones were ready for use. 



rig. 56 represents the circulatory apparatus of a worm four- 

 teen days old. It embraces two distinct systems : — (1) a closed 

 vascular system, consisting, as in the Annelids, of a dorsal and 

 ventral trunk, connected by lateral and terminal branches ; (2) a 

 lacunar system, consisting of a marginal sinus and a median 

 sinus, which communicates with the marginal sinus by means of 

 lateral branches, of which a single pair (right and left) is found 

 between each somatomere. The first system is coloured red, and 

 the second green. The median dorsal trunk, which alone js con- 

 tractile, takes a zigzag or meandering course just above~Ihe 

 alimentary tract. In the anterior third of the body it gives off 

 three pairs of lateral branches and one odd pharyngeal branch, 

 and just behind the eyes bifurcates, thus producing two cephalic 

 branches. The posterior pair pass outward and backward over 

 four pairs of diverticula (1 think they extend still farther back- 



