342 ON A HERMAPHRODITE AND 



above the bases of the feet, runs down to terminate on the ventral 

 surface, behind the last pair of thoracic appendages. From this 

 origin it extends as a wide free membrane beyond the setse, forming 

 an elegant collar around the head, on whose ventral surface the 

 expansions of each side unite, and form a wide reflexed lobe (fig. 4, 

 g), while posteriorly they remain separate. To the thorax succeeds 

 what may be called the abdomen, which is much longer than the 

 other regions of the body ; and is, besides, distinguished from them 

 by the imperfect development of the feet, and the paucity of 

 the setse and hooks. In this, and in the caudal portion of the 

 body, the relative position of the hooks and seta; is the reverse of 

 what it is in the thorax, the former being superior, and the latter 

 inferior.^ 



The caudal portion of the body is short, and wider than the 

 abdomen. Its rings are close-set, with well-developed hooks and 

 setae, and it is terminated by two conical papills between which the 

 anus is situated. There are not less than 50 rings in the whole body. 

 Cilia could be detected in active motion on many parts of the 

 external surface, on the bases of the feet, on the rudimental 

 tentacles, and scattered in tufts over the whole surface of the thoracic 

 expansions. 



Having thus sketched its external character, I will now pass to 

 the minuter features presented by the organization of the animal. 



Branchial plujiies. — The principal mass of these organs is formed 

 by a clear, firm, supporting axis, so marked transversely as very 

 closely to resemble the chorda of an Ainphioxus. The lower end of 

 this axis terminates by a somewhat pointed extremity, which lies in 

 immediate proximity to the oesophagus (fig. 4), and receives the 

 insertion of the lateral longitudinal muscles of the body. Superiorly, 

 as has already been said, the axis divides into four branches, one of 

 which enters the stem of each branchia and forms its skeleton and 

 support, sending lateral processes into each of the pinnules. These, 

 however, are much more delicate, and are composed of oblong 

 particles set end to end ; somewhat like the axis of the tail of an 

 Ascidian larva. All this branchial skeleton, as one might term it, is 

 invested by a continuation of the general parietes of the body, which 

 adheres closely to the outer side of the stem and pinnules, but leaves 

 a space on their inner side. In this space lies the so-called " blood "- 

 vessel, with its green contents. It does not fill the space, but lies 



^ According to Grube, this is the case in all the Serpulacea. See his most excellent 

 work — " Die Familien der Anneliden.'' 1851. 



