600 DR. H. CHAELTON BASTIAN ON THE ANATOMY AND PHYSIOLOGY 



These vessels (assuming them to be such) exist in the substance of the deep cellular 

 layer of the integument mostly in pairs, and extend from median line to median line. 

 They cannot be examined without careful preparation of the animal, of such a kind* as 

 to permit of the longitudinal muscles being entirely stripped from the surface of the 

 granulo-cellular layer after its body has been slit open in a longitudinal direction. The 

 best species for their examination is A. megalocephala, owing to the greater size of the 

 vessels and to the readiness with which, in their passage from median line to median 

 line, they may be traced through the substance of the lateral band. I have mapped out 

 inch by inch, as coiTCctly as possible, the entire series of these vessels as I found them 

 existing in a specimen of A. megalocephala (Plate XXV. fig. 10), and having examined 

 two other individuals in the same way, I found that they were distributed in the same 

 unsymmetrical manner — more than twice as many vessels existing on the right side of 

 the body as are to be met with on the left. And although I have not mapped out the 

 entire series in A. lumbricoides, I have ascertained that in this animal a similar dispro- 

 portion exists in the number of vessels found on the two sides of the body. I do not 

 think the number or relative positions of the several vessels is absolutely similar in 

 any two individuals of either of these species : small differences exist in different indi- 

 viduals, through a general similarity of arangement prevails. The general course of the 

 vessels may be best seen with a low power of the microscope, when they have the 

 appearance of bright undulating channels distinguishable by the total absence of 

 granules in their course through the dark granular membrane. Magnified to this extent 

 they seem mere lacunar passages only. They may generally be seen running in pairs ; 

 starting, for instance, from the dorsal median line at a short distance from one another, 

 we may see them pursuing an undulating course, either parallel with one another 

 or not, till we come to the lateral band, through which they may be seen to pass, gene- 

 rally external to the longitudinal vessel, and apparently unconnected with it in any way, 

 and then through the remaining tract of granular material till they reach the ventral 

 median line, where they may be either closer to one another or further apart than they 

 were at the dorsal line. As may be seen by the figure, during this course the two 

 vessels may cross one another either once, twice, or not at all ; they may keep at a pretty 

 uniform distance from one another, or may diverge widely. Where the vessels cross only 

 once, this most frequently occurs during their passage through the lateral band, and in 

 some cases they run so obliquely through this as to appear on the other side at quite a 

 different level from that at which they entered (Plate XXIII. fig. 7, and Plate XXV. 

 fig. 11). More rarely a single vessel may be seen pursuing this same course between 

 ventral and dorsal lines, and, rarer still, a single vessel stretches from one of the median 

 lines to the lateral band only, and there ends. These vessels have an almost unifonn 

 calibre throughout their extent, at all events no dilatations may be seen in their course 



* This may be most readily efFocted by maceration for about a week or ten days in dilute nitric acid. The 

 muscles require to be removed with great care, in order not to injure the layer in which the vessels are con- 

 tained. 



