OF HANGING DROPS 



257 



under which the shell of 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 revolution is symmetrically formed. 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 Orbulina is a simple spherical drop, Lagena suggests to 

 our minds a "hanging drop," drawn out to a long and slender 

 neck by its own weight, aided by the viscosity of the material. 



Fig. 8.5. (After Darling. 



Indeed the various hanging drops, such as Mr C. R. Darling shews 

 us, are the most beautiful and perfect unduloids, with spherical 

 ends, that it is possible to conceive. A suitable liquid, a little 

 denser than water and incapable of mixing with it (such as 

 ethyl benzoate), is poured on a surface of water. It spreads 



* 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 flacon que Ton remplit de nouveUe eau, on voit au bout d'une heure 

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

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

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

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

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

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

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



T. n. 17 



