l-'<i "Ti;i!l!A NOVA" KX I'KDTTTOX. 



tlic pi-ohoscis. It lias only ;i thin wall ventrall)- ami lalcfalK'. scpai'atiuL;' it from tlir 

 Mood-siuus, which is now a siiiok' U-shaped cavity, the two latcTal sinuses luiving 

 coalesced below. (Fip;-. ;',, II.) 



The lilood-sinus may be regarded as a, single cavity throughout, broken up bv 

 the encroachment of bridges of connective and muscular tissue, wliich appear (juite 

 irregularly, and arc not always symmetrical on the two sides. fmmediatelv after 

 passing behind the bi'ain, a median Acntral blootl-space is formed for a short distance, 

 as shown by M. .b)ubin (Fig- 4, A.). This, however, is soon divided again into two 

 lateral spaces (Fig. 4, B.), which liecome mcjre and more widely separated ]tv the 

 intervening mass of connective tissue (Fig. 4, C). This median space is ((uite distinct 

 from the vessel of the pr()lK>scis-sheatli, and instead of passing gradually into it, as 

 described by M. .Toubin. never has any connection with it whatever. This vessel. 

 usually called the dorsal vessel, th(jugh clearly belonging to the proboscis-sheath, is 

 a small cavity in the wall of the sheath itself, on the ventral side, appearing first 

 at the level of the hinder 2)art of the brain, and extending, probabh', throughout 

 the length of the sheath. Its dorsal wall anteriorly is a very thin and collapsible 

 membi-ane. Posteriorly the vessel sinks more deeply into the tissues below the 

 proboscis-sheath, so that its dorsal wall becomes much thick'cr. Not having cut a 

 whijle worm into sections (which would he a somewhat extensive undertaking), 1 am 

 unable to state what actually l)ecomes of this vessel at tlie hinder end : ])ut so far as 

 my evidence goes it is not, at any rate at the anterior end. in direct c()mmunication 

 with the other system of sinuses. To continue the history of the main system, as 

 we pass backwai'ds through the series of sections to the region where the mouth 

 and ft'sophagus appear, the lateral sinuses, at first few and large (Fig. 4, C), are 

 seen to spread round the outside of the oesophagus, so as to embrace it laterally 

 and dorsally, except for the interruption of the proboscis-sheath. They subsecjuentlv 

 become more and more subdivided by the bridges of connective tissue and muscles, 

 and at the same time smaller and less conspicuous. 



Finally, ])ehind the mouth, their condition is that of a network of (juite small 

 vessels almost completely surrounding the gut (Fig. 4, D.). Thev lie between the 

 inner longitudinal l)ody-muscles and the circular muscle-layer which surrounds the 

 gut, and have now acquired a much more detinite lining epithelium of their own. 

 They now present, in fact, exactly the appearance described and figured b}' ilul)recht 

 (1887, PI. XIII, fig. n). 



One other point may be mentioned in connection wilh the \ascular system, in 

 which I cannot entirely agree with M. Joubin's description (I'.HO). He states that 

 both in L. romn/afiis and in />. Iiaiiscni there are certain " orifices" by which the 

 cavity of the rhynchodseum is in c(miniunication with that of the I)loo(l-sinus i)i 

 the head. This communication is said not to be direct, hut cei-tain " ampulhv " in 

 the thickness of the wall of the rhynchodiicum are said to communicate througli a 

 kind of spongy tissue with I he Mood-.sinus, being at their inner ends in direct 



