496 MESSRS. T. B. JONES AND F. CHAPMAN ON THE 



and these must be useful. As this applies also to every species 

 in the direct line of descent, the characters which are sectional or 

 generic must also, at the time of their origin, have been useful. 



In the second place, although non-utilitarian characters do 

 undoubtedly appear in the normal course of variation, no agency 

 has yet been detected adequate to the extension of these useless 

 peculiarities to all the individuals which constitute a species, 

 and, further, to prevent their extension to any of the varieties 

 which are destined to become new species. Unless the power in 

 question can have this twofold effect it cannot lead, except by 

 a.ccident, to the production of useless specific characters. . 



Under conceivable conditions, however, it is possible that certain 

 useless characteristics may become limited to the individuals of a 

 single species. But what we know of the modes of variation 

 and the distribution of varieties indicates that, if at any time so 

 produced, they must be altogether exceptional and of the nature 

 of chance products ; and th5.t they cannot possibly constitute 

 such a general characteristic of species as has been suggested. 



Our final conclusion is that, whether we can discover their 

 use or no, there is an overwhelming probability in favour of the 

 statement that every truly specific character is or has been 

 useful, or, if not itself useful, is strictly correlated with such a 

 character. 



On the Kstulose PolymorpMncB, and on the Grenus Mamulina. 

 By T. EuPEET Jones, F.E.S., and F. Chapman, A.L.S., 

 F.E.M.S. 



[Eead 16th January, 1896.] 

 Part I. 

 The Fistulose Polymorphince. 

 It having been suggested that the several specimens referred to 

 the genus Mamulina, Eupert Jones, may possibly belong to 

 fistulose PolymorpJiincE,^ this memoir has been undertaken to 

 show what evidence there is for or against the suggestion. 



With this object in view, it is necessary for us to define the 

 special Polymorphince which bear extraneous growths of fistulose 

 form. Therefore, in the first place, we propose to take a survey 

 of the known fistulose, tubulose, and racemose Folymorphince. 



* F. B. Balkwill and F. W. Millett. — " The Foraminifera of Galway. 

 Journ. Microsc. Nat. Sci., vol. iii. 1884, p. 33. 



