VASCULAR SYSTEM. 115 



coat. There is thus in this system also a deviation from the type of the Lineidce, The size of 

 the vessels is proportionally larger than in the latter, and their transparent fluid contains a 

 number of minute corpuscles. In the living animal each lateral vessel contracts regularly 

 and swiftly from before backwards, sending a wave of fluid towards its posterior end, at 

 which the contraction ceases. A reversed movement by-and-by takes place, the contents 

 being propelled towards the snout. Anteriorly the two vessels course forward by the side 

 of the oesophageal portion of the alimentary canal without subdivision, pass along the sides 

 of the proboscidian sheath in special cavities (v), as in Lineus lacteus, in front of the former, and 

 reach the ganglia, where they communicate. A junction has not actually been seen posteriorly, 

 but analogy would lead us to suppose its existence. There appears to be little regularity or 

 rhythm in the movement of the fluid in these vessels, both occasionally contracting from before 

 backwards at the same time. Generally, however, the contractions are alternate. 



Whatever special function the oesophageal region may perform in regard to digestion, it 

 is clear the circulatory fluid bathing its outer wall is placed in a favourable condition for 

 oxygenation, as the mouth now and then must give entrance and exit to sea-water, under the 

 influence of the powerful ciliary currents caused by the entire surface of this division. Besides, 

 it is evident that during the varied actions of the oral aperture {e.g. during feeding) the circula- 

 tion would sometimes be much interfered with if such a rete mirabile did not exist. The special 

 branchial apparatus in the homologous region of Balanoglossus {vide poslea) also gives further 

 weight to our interpretation of the structure of the parts in this group. 



Dr. G. Johnston, (Ersted, and Dr. Williams mistook the ganglia for hearts, and the inferior 

 commissure for a connecting vascular trunk. The blood, says the latter author, derived from the 

 cutaneous system of capillaries, is poured by a dorsal vessel into one of the chambers of the heart 

 (the dorsal) . Erom the latter it is sent into the ventral cavity, and thence distributed over the 

 integumentary and intestinal systems. He, moreover, says the blood is red, and always devoid 

 of corpuscles. Such remarks are not based on correct observations. E. Blanchard in his 

 examination of Cerebratulus liguricus, describes the nervous centres as lodged in a cavity into 

 which the vascular trunks open, and this can only refer to the post-ganglionic lacunae, though 

 such do not by any means encircle the ganglia. I have not seen any vascular space surrounding 

 the " trompe " in front of the commissures, as described and figured by this author ; and the 

 fluid of the proboscidian cavity could only have been noticed there during the ejection of the 

 proboscis. He found numerous branches proceeding from the longitudinal trunks in his Cere- 

 bratulus liguricus. I cannot agree with M. van Beneden's views of the circulation in Lineus, for 

 he describes the lateral vessels as swelling into vesicles when they approach the ganglia, their 

 contents being conducted to the exterior by a ciliated funnel. The erroneous nature of this sup- 

 position has already been noticed under ' Cephalic sacs.' He also mentions that each lateral 

 trunk communicates only with that of the opposite side posteriorly, and concludes doubtfully 

 thus : — " Le long des parois du tube digestif, on voit en outre plusieurs vaisseaux, mais dont 

 les aboutissants sont difficiles a decourvir." Another deviation from accuracy is apparent from 

 his remark (under Cerebratulus (Erstedii) that " En arriere un gros vaisseau tres-large, a parois 

 tres-contractiles, qui parait et disparait par intervalles, occupe la ligne mediane et semble s'ouvrir 

 au bout de la queue." A reference to his figure and its explanation at once makes it apparent 

 that he has mistaken the proboscidian sheath for a blood-vessel. Prof. Keferstein again does 

 not enter into detail with regard to the circulation in Lineus, and his figures and descriptions 



