DR M'INTOSH ON SOME POINTS IN THE STRUCTURE OF TUBIFEX. 263 



reticulations. The latter quite differ from the long simple coils described and 

 figured by Dr Williams* in Nais filiformis, but doubtless he was misled by 

 their complexity. 



In some views, where congestion had been produced by the addition of 

 chloroform, atropine, or muriate of morphia,t the intestine was observed to 

 be covered by an extensive series of minute blood-vessels, longitudinal and 

 circular. This arrangement was due to the presence of two or three vessels in 

 each segment winding round the canal, and sending off lateral branches to meet 

 others from the adjoining trunks, as shown on the supero-lateral surface of 

 the intestine in Plate X. fig. 7, the ventral vessel in this case not being seen. 

 A series of nearly parallel anastomosing branches course from the secondary 

 trunk in a longitudinal direction. A lateral view of the seventh segment after 

 the addition of chloroform (Plate X. fig. 8) exhibits a much coarser reticulation, 

 in which the main trunks arise from the ventral. In such experiments, of 

 course, the trunks do not remain of their normal calibre, but are irregularly con- 

 tracted. These statements with regard to the vascular ramifications on the 

 surface of the intestine are fully borne out in the transverse and longitudinal 

 sections of the worm, the former exhibiting a complete mesh-work of blood- 

 vessels surrounding the alimentary canal in certain positions. The same has 

 been noticed by M. Perrier| in Dero obtusa, one of the Nais-grovop, and he 

 aptly compares the arrangement to a very elegant trellis with rectangular open- 

 ings. According to Mr Lankester they would appear to be more easily 

 observed in Chcetogaster. Under the action of chloroform, also, many fine 

 cutaneous branches were seen in Tubifex forming a network and a series 

 of parallel longitudinal vessels. These ramifications remained comparatively 

 still during the motions of the worm, and were probably fixed branches of the 

 perivisceral. Some of the twigs (which extended over most of the body-wall) 

 coursed towards the septa, and inosculated with the same set of vessels in the 

 adjoining segments. There is thus a series of vascular communications between 

 segment and segment independently of the main trunk. It would also appear 

 that some of the branches, which proceed from the dorsal towards the ventral, 

 do not join the latter trunk, but inosculate with twigs from the opposite side of 

 the body. 



The circulatory system in the elongated form (Plate X. fig. 9,) much 

 resembles that of the foregoing, though it is proportionally more developed. 

 The swollen periviscerals or " hearts " occur in the eighth segment, and 

 pulsate vigorously and alternately from eight to twelve times per minute. Very 

 slight contraction of the tissues anteriorly causes the mobile vessels to assume 



* Report Brit. Assoc, p. 182, PL III. fig. 8. 



The addition of a small quantity of this drug in solution was speedily fatal to ciliary action. 

 \ Ann. Nat. Hist. 4th Se. vol. 6, p. 264 (Extr. Comptes Rendus). 



