1i' I "TERRA NOVA" EXPEDITION. 



Cross" collections. Among them there are good series of sections of Linen* corrugatus, 

 Linetis hanseni, and Eupolia punnetti. I have worked through all the series, paying 

 particular attention to those (twelve in all) which were taken through the heads of the 

 worms, and which show the arrangement of the brain, cephalic organs, and blood-spaces 

 in that region. On carefully comparing all these series together, and also with the 

 "Terra Nova" specimens of L. I'ori'ngatti*, I can find no reason, either in the grosser 

 anatomy, or even in the finer details of histology, for regarding any of them as distinct 

 species, and I therefore consider them all synonymous with that originally described 

 by M'lntosh (187C>). 



One of the most characteristic features of L/m'itx r,>rrn</ittiix, as has been noticed 

 by M. Joubin (1910), is the arrangement of the large blood-sinuses in the head. 1 

 have paid special attention to this system in all the species mentioned, and find it in 

 everv instance identical. Such slight apparent differences as there are, are evidently 

 the result of different states of contraction, and are in no way due to any variation in 

 structure. At the point where the blood-sinus traverses the nerve-collar it becomes so 

 compressed in some specimens as to be almost obliterated, but it can nevertheless be 

 traced, and shown to go through essentially the same changes at different levels, in all 

 the specimens examined, and in all the "species" above named. 



As my conception of this blood-sinus and its transformations differs somewhat in 

 details from that of M. Joubin (1910), and as it is an important feature of the species, 

 1 have prepared a series of diagrams illustrating its appearance as it is traced back 

 through any series of transverse sections, commencing with the snout of the animal. 

 These diagrams were all outlined with the camera lucida, though they were not all 

 taken from the same series of sections, as the vessels in a given region were better 

 displayed sometimes in one specimen, sometimes in another, according to its state of 

 contraction. In all, however, they could be traced with more or less ease, and reduced 

 to the same plan. 



Starting, then, with the tip of the animal's head, we find a, single blood-sinus 

 occupying a median position dorsal to the rhynchodseum (Fig. 3, A.). This sinus soon 

 widens out (Fig. 3, B.), and becomes divided into two lateral spaces by the develop- 

 ment of a partition from the dorsal side of the rhyneliodanim to the opposite wall of 

 the sinus (Fig. 3, C.). The blood-spaces, a little behind this point, come to embrace 

 the rhynchodajum between them, each being of a crescentic shape in transverse section 

 (Fig. 3, D.). This condition remains constant until the region of the brain begins 

 to be reached. The connective and muscular tissues in the centre now begin to 

 increase at the expense of the blood-spaces, which become very attenuated (Fig. 3, 

 E.-H.). This development of muscular tissue is the first indication of the proboscis- 

 sheath proper, whose muscles are at this point continuous with those of the proboscis 

 itself. 



A space, or spaces, now begin to appear in the central tissue. These represent 

 the beginning of the lumen of the proboscis-sheath, which soon completely surrounds 



