VEIN. 



1383 



and consists of branched cells, of a black 

 colour, and various form. The body of the 

 cell is generally some modification of an oval 

 or oblong, and lies with its long axis corres- 

 ponding to that of the vessel ; and from its 

 extremities caudae project, of every imaginable 

 shape and proportion, of larger size than 

 those which project from its sides, which are 

 few and small. The body of each cell appears 

 to be occupied by its nucleus. 



667. 



Veins from Fish exhibiting Pigment cells. 



A, vein from muscle of eel (Anguilla acutirostris) 

 {Magnified 50 diameters). B. vein from muscle of 

 sole (Solea vulgaris) (Magnified 100 diameters). 

 c, little mass from the external surface of the car- 

 dinal vein of the eel (Magnified 200 diameters.') 



In the accompanying figure, some of these 

 cells are represented from the eel (Anguilla 

 acutirostris}, and sole {Solea vulgaris), which 

 present considerable variety of form. They 

 also vary in the same individual in different 

 situations : in the cardinal vein they are most 

 numerous and aggregated ; in smaller veins 

 they are less numerous and more distinct ; 

 and in those of minute size, they only occur 

 here and there at considerable intervals, and 

 at the spots where they are placed they 

 occupy nearly the whole face of the vessel. 



When submitted to high microscopical 

 power, these cells are seen to be mixed up 

 with the tissue of the venous coats, and their 

 thin branched extremities have, in some places, 

 much the aspect of elastic tissue, in the uni- 

 formity of their dimensions and their dicho- 

 tomous divisions. 



Caudal venous heart of eel. Dr. Marshall 

 Hall, in 1831, first figured and described a 

 peculiar pulsating organ which exists in the tail 

 of the eel, calling it by the name of "caudal 

 heart ; " and he considered it to be a muscula.r 



ventricle, by whose contractions the blood is 

 propelled in the vein at the commencement of 

 which it is placed. 



Rusconi has differently interpreted this 

 organ, and calls it a lymphatic heart, believing 

 that it is perfectly analogous to those pul- 

 sating sacs, which are found in certain parts 

 of the 1} mphatic systems of various reptiles. 

 And certainly the occurrence of a little pul- 

 sating organ, having the form, colour, and 

 general aspect of the lymphatic hearts in the 

 frog, situated in the vicinity of the venous 

 sysfem, having an action independent of the 

 systemic heart, and existing in a cold-blooded 

 animal, is, from analogy, enough to suggest 

 the idea that Rusconi's view is the correct 

 one. But this is not confirmed by anatomy, 

 for after repeated and numerous observations 

 of this heart, I am convinced that the original 

 description of it, given by Dr. Hall, is the 

 truth. 



The caudal heart is to be found in eels of 

 all sizes, but is best seen in small individuals 

 a few inches in length, on account of their 

 clear skin, and the larger proportional size of 

 the organ in them. It may be seen by holding 

 the eel's tail between the light and the eye of 

 the observer, either with a lens, or without the 

 aid of any magnifying power. It may be con- 

 veniently examined with the microscope by 

 wrapping the head of the animal in a wet cloth, 

 and then applying its tail to a slip of glass, and 

 placing it under the field of the instrument ; but 

 the extreme restlessness of the little fish some- 

 times renders it necessary that it should be 

 partially or completely stunned before it can 

 be viewed. The heart is then seen to be 



fig. 868. 



Caudal Venous Heart of Eel magnified about 25 

 diameters. 



A and B represent two forms, a, the heart : b car- 

 dinal vein ; c sinus that receives the blood from 

 the capillaries; </, minute veins from caudal tin. 



placed near the extremity of the cardinal vein, 

 on the haemal aspect of the caudal vertebrae 

 at the end of the tail. It is of a yellowish 

 colour, chequered more or less with stellate 

 pigment, and of a form varying from a pear- 

 shape to a spindle-shape. (Fig. 868.) At 

 the distal extremity it is connected with a 

 small vein, which collects the blood from the 

 capillaries of the tail ; at its proximal ex- 

 tremity it is connected with the commenc- 

 ing cardinal vein ; or it may be said that on 

 4 T 4 



