V] OF HANGING DROPS 415 



force of perfect symmetry. Save for one or two other forms which 

 are also spherical, or approximately so, like Thurammina, the rest 

 of the monothalamic calcareous 

 Foraminifera are all comprised by 

 naturalists within the genus 

 Lagena. This large and varied 

 genus consists of "flask-shaped" 

 shells, whose surface is that of an 

 unduloid, or, hke that of a flask 

 itself, an unduloid combined with 

 a portion of a sphere. We do 

 not know the circumstances under 

 which the shell oi Lagena is formed, 

 nor the nature of the force by 

 which, during its. formation, the 

 surface is stretched out into the 

 unduloid form; but we may be 

 pretty sure that it is suspended 

 vertically in the sea, that is to 

 say in a position of symmetry as 

 regards its vertical axis, about 

 which the unduloid surface of re- 

 volution is symmetrically formed. 



4 5 6 



Fig. 131. Roman pottery, for comparison 



with species oi Lagena. E.g., 1, 2, with 



L. sulcata; 3, L. orbignyana; 4, L. 



striata; 5, L. crenata; 6, L. stelligera. 



At the same time we have other 

 types of the same shell in which the form is more or less flattened ; 

 and these are doubtless the cases in which such symmetry of position 

 was not present, or was replaced by a broader, lateral contact with 

 the surface pellicle*. 



While Orhulina is a simple spherical drop, Lagena suggests to our 

 minds a hanging drop, drawn out to a longer or shorter neck by 



* That the Foraminifera not only can but do hang from the surface of the 

 water is confirmed by the following apt quotation which I owe to Mr E. Heron - 

 Allen: "Quand on place, comme il a ete dit, le depot provenant du lavage des 

 fucus dans un fiacon que Ton remplit de nouvelle eau, on voit au bout d'une heure 

 environ les animaux [Gromia dujardinii] se mettre en mouvement et commencer 

 a grimper. Six heures apres ils tapissent Texterieur du flacon, de sorte que les plus 

 eleves sont a trente-six ou quarante-deux millimetres du fond; le lendemain 

 beaucoup d'entre eux, apres avoir atteint le niveau du liquide, ont continue a rarnper 

 a sa surface, en se laissant pendre au-dessous comme certains mollusques gastero- 

 podes." (F. Dujardin, Observations nouvelles sur les pretendus cephalopodes 

 microscopiques, Ann. des Sci. Nat. (2), iii, p. 312, 1835.) 



