1890-91.] A '' Colonial" Herbarium specimen. 473 



rock — not only such rocks as tlie microscope reveals to be com- 

 posed of them, hut also such as have become changed, so as 

 no longer to show their forms. Large tracts of the bottom of 

 the Atlantic, at or about 2400 fathoms, are covered with the 

 spherical tests of the now familiar form, Globigerina, the 

 deposit being termed Globigerina ooze. 



Here and there on our specimen the microscope also detects 

 groups of transparent threads with the vestiges of terminal 

 cups. These are the remains of the once extremely sensitive 

 and active infusorian, Vorticella. Infusoria include many 

 forms so closely akin in form and function to certain minute 

 algte and fungi, that it is a matter of extreme difficulty to 

 distinguish where the boundary-line between the plants and 

 animals should be fixed. Vorticella, the bell-animalcule, is 

 distinct enough. Elevated on a delicate stalk, which is cap- 

 able of extremely rapid spiral contraction, is a bell-shaped 

 head, having a crown of cilia which vibrate in such a manner 

 as to convey the idea of continuous rotary motion. At one 

 side of the crown there is a mouth, into which food is swept 

 by the vortices caused by the coronal cilia. A ciliated jjassage 

 leads inwards and terminates blindly. The food is engulfed by 

 the gelatinous body-substance, and then digested. A nucleus 

 and a vacuole can be made out, the latter showing pulsating 

 contraction and expansion. Multiplication takes place by 

 simple fission of the bell, or by conjugation between individ- 

 uals unequal in size, followed by division. 



Hitherto we have dealt with animal forms too minute to 

 Idc seen by the naked eye ; now we have to deal with a re- 

 latively huge structure, forming, indeed, the most prominent 

 object on the sheet. It is a sponge known as Grantia com- 

 pressa, hanging from the Delesseria as a white, leathery, 

 flattened sack, half an inch in length. Mr Lindsay has so 

 recently described this species in his most interesting paper 

 on the sponges, that it is unnecessary to dwell on its struc- 

 ture. Our ideas of sponge structure are generally taken from 

 the contemplation of the household article, and most people 

 have therefore a difficulty in believing that a sponge may be 

 found to be virtually composed of sharp, three-rayed, cal- 

 careous spicules. Such, however, is really the condition of 

 Grantia. In the living state of the sponge, as was pointed 



VOL. II. 2 I 



