63G MR. E. R. LANKESTER ON SOME LOWER ANNELIDS. 



prostomium, whilst a larger number pass posteriorly, forming a sort of network on the 

 pharynx, with the substance of which they appear to fuse. Leydig has figured the 

 anterior nerve-twi^s as terminating in oval nucleated cells ; but this I have not found 



. e ~ ^ „^..^^ — ^ 



to be the case. The enlargement which underlies the oesophagus proper is a flattened 

 lobular mass, giving off two principal horizontal trunks, one on either side (fig. 25); 

 posteriorly to this the nervous system becomes very obscure. The lobulated tissue 

 on the pharynx, which forms the ganglia and surrounds the cord at different points, 

 appears to represent cellular nervous tissue; it branches out in various directions, and 

 breaks up into little twigs. Occasionally small clear cells with nuclei may be seen 

 scattered in its substance; but the character of the nervous tissue in these immature 

 forms is that of a homogeneous protoplasm. 



In the production of zooids it appears that the element of the ventral cord remains 

 continuous throughout the chain until a separation is very shortly about to occur. 



The Vessels and their Fluid. — The extensive system of vessels to be detected in Chce- 



togaster Umnai, identical with the closed system of vessels in all Annelids but the 



Leeches, which are not rightly called Annelids, contains a colourless fluid. The red fluid 



of other Annelids contains red cruorine, and is undoubtedly efficient in respiration ; so, 



too, this colourless fluid contains a respiratory medium (an oxygen-carrier) like green 



or red cruorine, though colourless, and is, as are the colourless vascular fluids of other 



Annelids, efficient in respiration. The minuter ramifications of the vessels may be 



detected by a curious optical property presented by fluids in exceedingly narrow tubes, 



namely, their pinkish or purple tint*. The fluid in larger vessels appears (as it is) quite 

 colourless. 



The vessels which distribute this fluid over the body are diflicult to trace out fully; 

 but in this species I do not find the arrangement to be the same as that described by 

 Leydig in his < Lehrbuch,' where he gives a diagrammatic figure of some of the vessels of 

 Cluztog aster. We have, in the first place, what may be a peripheral capillary network 

 traversing the whole surface of the integument, and performing the inspiratory function 

 of the worm. We have a second or intestinal capillary network, apparently not provided 

 ith such minute branches (figs. 12, 13, 14). I have only been able to make out two sreat 



longitudinal trunks-a dorsal and a ventral. The dorsal is a powerful and highly 

 tractile vessel, giving off the large branches to the intestinal system, and probably also 

 to the tegumental, peripheral, or respiratory system ; but this I have not seen. At 

 the region of the cesophagus it gives off on either side a highly dilatable coiling vessel, 

 which joins the ventral trunk ; each of these represents one of the moniliform « hearts " 

 of the earth-worm. The dorsal vessel itself passes on, giving off numerous branches 

 on the surface of the pharynx, and, passing beneath the suprapharyngeal nerve-collar, 

 breaks up into two large lateral trunks, and also into small stems which form a vascular 

 ring round the mouth (figs. 12, 14 l P v). The two lateral vessels pass down the neural sur- 



pulsatxng cavxhes of Infusoria, and in the minuter ramifications of the eanalicnli 

 teeth. Dr. Zenker, in a recent number of Max Schultze's Archiv (Bd. ii., p. 332) 

 Infusona, and asenbes it to the law of complementary colours, the substance of the I 





