36 GEORGE OSSIAN SARS. 



nected with the contractile cord, and is produced only by a 

 peculiar modification of. its tissue on the ventral side. Special 

 retractor muscles cannot, therefore, any more than other 

 muscles, be said to be distinguished in the Rhahdopleura. 



Through all the creeping stem there extends, as already 

 mentioned, a filiform cord, very remarkable by its dark, 

 nearly black colour, and, unlike the contractile cord, to 

 which it is about equal in thickness, only slightly flexible, 

 and of a very hard, chitine-like consistency. This cord (figs. 

 5, 6, &c., i), which we will call the axial cord (" chitinous 

 rod," Allman), is freely extended in the hollow of the indi- 

 vidual chambers into which the stem is divided, and only 

 attached to the septa, which it perforates, enlarging itself a 

 little. In conformity with the rarely branched form of the 

 stem, it is only now and then forked, and when this takes 

 place, it is always at one of the septa. Otherwise, it forms 

 everywhere a cylindrical tube with very strong, almost horny, 

 walls, but alwa3's enclosing in its interior a soft, cellular cord (s), 

 of similar appearance to the contractile cord, and, like it, colour- 

 less and transparent, with small dark violet spots of colouring 

 matter, but scarcely half so thick. This fine cellular marrow, 

 which extends through the whole length of the axial cord, 

 seems entitled to be considered as a sort of incompletely 

 defined nervous trunk, connecting all the individuals of the 

 colony, as at each partition in the stem it sends forth a 

 branch, which enters into the contractile cord of each re- 

 spective individual animal ; and the latter cord does also 

 probably contain in its dorsal part the imperfectly developed 

 elements of nerves. We may, therefore, herein observe the 

 analogue of the so-called colonial nervous system (so strongly 

 developed in the other marine Polyzoa), and specially in the 

 marrow of the axial cord, the common main trunk of the 

 whole colony. 



Allman, who has drawn special attention to this peculiar 

 chitinous axial cord (which does not exist in any of the 

 known Polyzoa) , and has precisely derived from it his generic 

 appellation, calls it a " blastophore,'' being of opinion that 

 it is destined to bear the so-called statoblasts, which he 

 represents as projecting from the posterior part of the con- 

 tractile cord. I regi'et that I cannot, from ray own ex- 

 perience, give any decided opinion as to the axial cord having 

 likewise this destination, because I have not been able to 

 observe the formation of these so-called statoblasts. 



The animal, unlike the other Polyzoa, is very slightly 

 sensitive, and is not much affected by having its tentacles or 

 body touched. If the irritation is strong, it draws itself, 



