26 GEORGE OSSIAN SARS. 



continuously with, the cavity of the stem. This latter, the 

 interior walls of which, like those of the tubes, are quite 

 smooth, is divided at certain intervals by tolerably thick 

 transverse lamellae, or septa, into several successive cylindrical 

 chambers, which do not communicate with each other, but 

 each one of which is continued immediately in one of the 

 perpendicular tubes proceeding upwards from the stem. 

 Through the whole of the creeping stem, extending along 

 through all its chambers, runs a thin cylindrical chitinous 

 cord (the axial cord), very remarkable from its dark, nearly 

 black, colour, of which more hereafter. This cord is never 

 continued up through the free tubes, but may now and then, 

 rarely, divide itself fork-wise, namely, when the creeping 

 stem divides itself in this manner. 



Every one of the perpendicular branches or tubes contains 

 an animal, which is connected by a long, cylindrical, fleshy 

 cord (the contractile cord), near the bottom of the corre- 

 sponding chamber in the stem, with the axial cord, which 

 thus unites all the individuals of the colony with each 

 other. 



The creeping stem in the R. mirabilis may indeed attain 

 a very considerable length, but it is very difficult to get the 

 whole separated from the substances which adhere to it. 

 One can usually, therefore, only get up small pieces of the 

 colony, and seldom more connected portions. The largest 

 connected piece of stem which I succeeded in getting 

 loose from its attachment was about 40 mm. long, and was 

 at irregular distances four times bifurcated ; another piece 

 was of about the same length, but only three times divided. 

 These branches, which proceed from the stem at a more or 

 less acute angle, are also creeping and irregularly bent, and, 

 like the main stem, produce cells, the number of Avhich in all 

 on these pieces of stem amounts to about 60. The stem is 

 thus only seldom branched, and usually runs to great length 

 without producing any branch. 



The cells or tubes, which proceed from the stem by lateral 

 budding, are of very difi'erent length, while their thickness is 

 everywhere, and in all, about the same. The largest are 

 6 — 7 mm. long and \ — i mm. thick. They are, as stated, 

 erect, yet seldom, or never perfectly straight, but always 

 more or less bent in some part, or in the whole of their 

 length, sometimes like an S, sometimes in several bends or 

 turns, like a drawn out screw, but most frequently irregularly 

 bent, in rare instances so strongly curved, that the curve is 

 nearly circular. 



From the above description, it will be seen that the poly- 



