EUCRATEA. 13 



growth. The two are essentially identical in struc- 

 ture. 



The creeping base exhibits some curious modifications 

 in this genus. When it is developed on the stems of the 

 more slender Algae, it consists universally, so far as I have 

 seen, of lines of decumbent cells, from which the erect 

 shoots rise, originating, like the ordinary branches, a little 

 below the aperture. But in other cases I have found it 

 assuming the form of a delicate tubular fibre, like that of 

 Aetea, which at intervals swells out into small clavate 

 enlargements, from which the cells arise. I have never 

 seen the passage of one of these conditions into the other ; 

 but it is difiicult to avoid the conclusion that they are 

 morphologically equivalent, and that the clavate enlarge- 

 ments are merely aborted cells. They are frequently 

 much attenuated in Eucratea, sometimes almost oblite- 

 rated ; and in such cases we have an indication of the way 

 in which the chain of adnate cells passes into the per- 

 fectly simple tube. Under E. chelata I have described 

 a curious variety, in which the decumbent condition of 

 the zoarium appears to be permanent. 



Two species of Eucratea, as now defined, have been 

 described. One of them, E. ambigua, D^Orb., which 

 closely resembles the present form, is a native of South 

 America. E. chelata has a wide distribution in Europe, 

 while in Austraha it is exceedingly abundant, attaining a 

 size and beauty which are unknown in our seas. 



Busk has described a Polyzoon from Madeira under the 

 name of Scruparia [ = Eucratea) diaphana* ] but, from 

 its mode of branching and the size of the aperture, it 

 would seem to be more properly referable to some other 

 genus. 



* Quart. Journ. Micr. Sc. (n. s.) \iii.,Zoopbytol. 281, pi. xxxi. figs. 1, \a. 



