Ijr, "TKHHA NOVA" EXPEDITION. 



the proboscis. It has only a thin wall ventrally and Literally, separating it from the 

 blood-sinus, which is now a single I T -shaped cavitv, the two lateral sinuses having 

 coalesced below. (Fig- 3, H.) 



The lilood-sinns may lie regarded as a. single cavity throughout, broken up bv 

 the encroachment of bridges of connective and muscular tissue, which appear quite, 

 irregularly, and are not always symmetrical on the two sides. Immediately after 

 passing behind the brain, a median ventral blood-space is formed for a short distance, 

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

 lateral spaces (Fig. 4, B.), which become more and more widely separated by the 

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

 from the vessel of the proboscis-sheath, and instead of passing gradually into it, as 

 described by .Al. Joubin, never has any connection with it whatever. This vessel. 

 usually called the dorsal vessel, though 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 part of the brain, and extending, probably, throughout 

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

 membrane. Posteriorly the vessel sinks more deeply into the tissues below the 

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

 whole worm into sections (which would be a somewhat extensive undertaking), I am 

 unable to state what actually becomes of this vessel at the hinder end ; but so far as 

 my evidence sroes it is not, at anv rate at the anterior end. in direct communication 



J O J 



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

 we pass backwards through the series of sections to the region where the mouth 

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

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

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

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

 and at the same time smaller and less conspicuous. 



Finally, behind the mouth, their condition is that of a network of quite small 

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

 inner longitudinal body-muscles and the circular muscle-layer which surrounds the 

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

 They now present, in fact, exactly the appearance described and figured by Hubredit 

 (1887, PI. XIII, fig. 6). 



One other point may be mentioned in connection with the vascular system, in 

 which I cannot entirely agree with M. Joubiu's description (1910). He states that 

 both in L. i-orruijatnx and in L. hanxt'iii there are certain "orifices" by which the 

 cavity of the rhyuchodamm is in communication with that of the blood-sinus in 

 the head. This communication is said not to be direct, but certain " ampulhu " in 

 the thickness of the wall of the rhynchodseum are said to communicate through a 

 kind of spongy tissue with the blood-sinus, being at their inner ends in direct 



