MYRIANIDA. 81 



ing vessels of the gills. Usually there is, in worms of this kind, 

 one vessel which is larger than the others, and which runs above 

 them, in a straight line, to a greater or less extent, along the back 

 of the intestine. This is usually called the heart. On the lower 

 side of the body, and along its middle line, there runs a nervous 

 cord, which is swollen into knots or ganglions, as they are called, 

 in each joint. The principal ganglion (the brain) of this organ, 

 is situated in the head (H) above the intestine, and is joined to 

 the ventral cord by a sort of collar, the nervous collar so called, 

 which embraces the throat. The reproductive organs are to be 

 met with only in the posterior rings of the body, and are lo- 

 cated there apparently in reference to the peculiar mode of 

 reproduction which I am about to describe. 



Nearly a century ago a Danish naturalist, Miiller, had observed 

 that a certain marine worm divided itself into two parts, and 

 in some instances into four, and that each part continued to live 

 after the separation. He moreover noticed that the anterior or 

 oldest part of the worm did not contain any eggs, but that the 

 latter were altogether confined to those parts which separated 

 from it. Later observers, in several instances, have confirmed 

 the statements of Miiller, and, among others, Milne Edwards 

 has added largely to our knowledge of this phenomenon by his 

 elaborate investigation of the sixfold fissigemmation* of Myrian- 

 ida. He noticed, what Miiller had already mentioned, that, where 

 more than one young individual was formed, the oldest was 

 always the last (1) ; but what made the case the more striking 

 in Myrianida, was that there were no less than six young devel- 

 oping at one time, and that they were, in regular succession (6, 

 5, 4, 3, 2, 1), older as they were farther from the head of the 

 original stock. Each was possessed of a pair of eyes at the 

 anterior end, and of a certain number of rings or joints. Thus 

 the youngest (6) had ten joints; the second (5) fourteen; the 



* A word compounded of Jissus, divided, and gemmatus, budded ; in allusion to 

 the peculiar process here involved, which consists of a growth by budding, and a 

 multiplication of individuals by the division of the compound body. 

 6 



