156 Proceedings of the Royal Irish Academy. 



Quite apart from our specific triangles and the nebulous No Man's Land 

 occupied by .rxx (the intermediate specimens) are tliose rare monstrosities 

 in which the organism appears to pass at a bound from its immediate 

 congeners into a far distant group. These monstrosities constitute the 

 teratology of the Foraminifera, and up to the present have received little 

 attention. For the purposes of the present paper they may be almost dis- 

 regarded, but a closer study of such monstrosities may, perhaps, in the future 

 afford the solution to many problems. 



It is the object and purpose of tliis paper to attempt to throw some light 

 upon the origin of biological characters and variations in tlie Foraminifera — 

 in a phrase, to explain, or at any rate to suggest, how these new biological 

 charactei-s have their origin, are evolved, and transmitted ; and we propose to 

 illustrate this attempt by a description of the results obtained by the cultuie 

 of two species of Foraminifera, both of common or almost woild-wide occur- 

 ence, and phylogenetically (according to existing systems of classification) 

 almost as widely separated from one another as is possible, viz , Massilina 

 serans (d'Orbigny) and VernaiUina poli/Mroiiha (Eeuss). 



Before entering upon the description of our experiments it is necessary Lo 

 call attenlion as sliortly as possible lo tlie modificaLions or variations of 

 biological charactei-s whicli have already been recognized in the Foraminifera, 

 and to some other conditions to whicli we take tliis opportunity of calling 

 attention for the first time. 



Tiie three forms of variation in the Foraminifera which have already been 

 recognized (apart from isomorphism) are — 



1. Variation in the size of the primordial chamber, including its influence 

 on the aftergrowth of the test. 



2. Variation in the plan or arrangement of chambers in difl'erent stages of 

 the life-history of the Foramiuifcr. 



3. Variation of external form, or simple " variation." 



In addition to these, we propose to offer a few remarks on certain forms 

 of variation and habit which have attracted little attention hitherto : — 



4. The occurrence of gigantism and nanism. 



5. Chitinons variation. 



6. Variation due to sessile habitat of a normally free form, or vice versa. 

 11. " Encryptment ": excavating or burrowing Foraminifera. 



(i) The leading variation, concerning which a great deal has been written, 

 is the problem of the co-existence in a species of individuals differing 

 essentially in the size of their primordial chambers, which, under the now 



