V. 



Fj,.. 3. — Lineus conugatus. — Diagrams of a series of transverse sections, illustrating the vascular system, 

 which has been represented in solid black. The brain and nervous structures are hatched. 

 Pr., proboscis ; P.S., cavity of proboscis-sheatli ; /?., rhynchodieum, .seen opening to the exterior 

 in the first diagram (A). 



A — Shows the median blood-sinus in the snout, lying dorsally to the proboscis-pore (R,). Blood-sinus represented 

 in solid black. 



B — The proboscis-pore has passed into the rhynehodseum (/?.), and the blood-sinus is of wider calibre. 



C — The blood-sinus becomes divided into two Ijy a partition of connective tissue developing on the dorsal side. 



D — There is now a complete wall of coimective and muscular tissue dividing the two blood-spaces, and enclosing the 

 rhynchod«um. 



E — Nerves from the anterior part of the brain are appearing laterally, and the central tissue is encroaching more and 

 more upon the blood-spaces, so as to reduce them in size. 



F — The central muscular tissue begins to show spaces — the beginning of the cavity of the proboscis-sheath (P.S.). 

 Blood-spaces still further reduced. 



G — The cavity of the proboscis-sheath is now seen completely surrounding the proboscis (Pr.). and separated by a thin 

 wall from the blood-space on either side. The blood-spaces are pressed between the brain and the proboscis- 

 sheath, so as to be very narrow at this point. 



H — The blood-spaces have coalesced ventrally, so as to form a L'-shaped vessel enclosing the proboscis-sheath. 



