354 



The vascular system. The vascular system of Thalassema 

 Neptuni is essentially the same as that described by Greeff in Echiurus. 

 The same loop is formed around the oesophagus, and a second around 

 the muscles of the setae as in Echiurus^ and the same main trunks are 

 present, but the trunk which runs along the posterior part of the in- 

 testine is in Thalassema degenerate if not actually obliterated. The 

 brilliant orange colour of the outer wall of the vascular trunks renders 

 them very obvious as in Echiurus. The fluid within the vessels is 

 colourless and does not contain corpuscles similar to those of the 

 perivisceral fluid. Claus states that the vascular liquid is coloured in 

 some Gephyraeans, but if we except Phoronis^ I known of none in 

 which this is the case, for in Sipunculus the liquid of the short vascular 

 trunks is not a special liquid but identical with the perivisceral liquid. 



Cloacal pouches. A chief object which I had in view in 

 examining living specimens of Thalassema was to determine whether 

 Greeff is justified in stating that the »ciliated funnels« or »cups« on 

 the coelomic surface of the cloacal pouches do not open into the cavity 

 of those pouches. The cloacal pouches of Thalassema are exceedingly 

 irritable and contractile, so that alcohol causes them to shrink and 

 further when a piece is cut out from a living specimen for examination 

 under the microscope, the pieces immediately contract. This contrac- 

 tion necessarily prevents one from seeing the funnels opening on the 

 inner face of the pouch, supposing such to exist. At the same time 

 very frequently when I had pinned out a Thalassema in sea-water, 

 with the body-wall reflected so as to expose the viscera, the cloacal 

 pouches were seen to be greatly distended and their walls quite trans- 

 parent instead of thick and corrugated as they are when contracted. I 

 found that by injecting osmic acid solution (2^0) into the expanded 

 pouch through the cloaca it was possible to arrest all movements of 

 contraction and thus to obtain the wall of the pouch in an extended 

 condition for examination with the microscope. I found on careful 

 study of preparations obtained by this method that each of its fun- 

 nels does most certainly open into the cavity of the 

 cloacalpouch by a very minute pore, which it would be im- 

 possible to see unless the wall of the pouch were fully extended so as 

 to make it smooth and transparent. The diameter of the aperture 

 which lies at the base of the cup or funnel on the inner surface of the 

 pouch was in Thalassema Neptuni, only Veooo*^ of an inch. Consequently 

 though liquid passes through these stomata driven inwards by the 

 action of the cilia, none of the corpuscles of the perivisceral liquid can 

 traverse them. 



The canal system which Greeff has supposed to exist in 



