518 



SYSTEMATIC HISTORY OF THE INFUSOEIA. 



investment (the envelope-cell). Each cell or gonidiiim has its own hyah'ne 

 membrane, is somewhat elongated into a neck-like form on one side, and con- 

 tains a homogeneons protoplasm, chlorophyll, and dark granules (except in the 

 neck-hke portion), and in the centre a single chlorophyll vesicle ; besides these, 

 several vesicular spaces, and one, two, or rarely three contractile vesicles. 

 From the pointed end two filaments proceed, and pierce the common envelope, 

 to vibrate freely on the outside of the tablet. Reproduction by fission is not 

 a simultaneous act, as represented by Ehrenberg, but is effected by repeated 

 divisions through four generations or series, in each of which the ' daughter 

 cells' severally resolve themselves into two others, as happens in all the Yol- 

 vocina andPalmelleae. The result of this act of reproduction, when uninterfered 

 with and complete, is the fonnation of sixteen tablets similar to the parent, 

 but without any organic connexion, each yoimg tablet, however, being enclosed 

 within the wall of the parent cell, out of which it has been produced, for this 

 cell-wall takes no part in the process of fission. Sometimes a tablet breaks 

 up, setting its component gonidia free, when, their angular processes becoming 

 absorbed, and their membrane further removed from the contents, they as- 

 simie the general aspect of a Chlami/dococcus or Chlamydomonas, and probably 

 enter on a resting-stage like the gonidia of Stephanosphcera. Ehrenberg be- 

 lieved the isolated cells to be reproduced by fission like those united in the 

 tablets ; but Cohn never observed this take place. If this resting-stage actually 

 occurs, then Gonium is projpagated by ' macrogonida' ; but of ' microgonidia' no 

 evidence has been discovered. The tablets revolve on their shorter axis, and 

 hence, on a polar aspect, appear lilte a disk, on an equatorial like a line of 

 cells. A peculiar structural relation obtains between Oonkmi and Pedias- 

 trum. Lastly, Cohn asserts that Gonium Pectorcde is the only true species of 

 this genus ; that the others enumerated by Ehrenberg are motionless, and 

 belong to the genus Merismopedia among the Palmellaceae. 



Gonium Pectorale (M.) (see p. 152). 

 — Consists of sixteen spherical bodies 

 enclosed within a transparent lorica, and 

 disposed regularly in a quadrangular 

 form, and in the same plane, like the 

 jewels in the breast-plate of the Jewish 

 High Priest, whence the specific name. 

 The four central ones are generally larger 

 than those which surround them; and the 

 combined diameters of the three smaller 

 balls are about equal to the two larger 

 centre ones to which they are attached ; 

 the external corners are consequently 

 vacant. As these animalcules swim and 

 revolve in the water, they occasionally 

 present a side view to the observer, when 

 the circimiference of the larger central 

 globides may be seen projecting beyond 

 the others. Sometimes the clusters ap- 

 pear irregular. They are of a beautiful 

 transparent green colour ; and in swim- 

 ming, the globules often appear of an 

 ellipsoidal figure. 



In order to observe the structure of 

 tliis highly curious and beautiful crea- 

 tm'c, considerable adroitness is necessary 

 in the management of the microscope; 

 while a little indigo conveyed into the 

 water with the point of a cameFs-hair 



pencil wUl be required to see the whorls 

 and currents set in motion around it. 



The single animalcules (xrx. 33) swim 

 like the Monads, in the direction of the 

 longitudinal axis of their bodies ; but the 

 tablets have a variety of movements: 

 sometimes they move quite horizontally, 

 at others vertically, at others again on 

 their edge, revolving like a wheel. A 

 magnifying power of 200 diameters is 

 sufficient for general examination ; but 

 to exhibit aU the structm-es shown ia 

 the engravings, fom' times that power 

 will be required. In clear water, salt 

 and fresh, near the surface. Discovered 

 by Miiller in clear water at Copenha- 

 gen, 1773. Size of animalcide from 

 1-460" to 1-1150", of tablet not exceed- 

 ing 1-280". 



G. jmnctatimi. — Corpuscles green, 

 spotted Avith black, and enclosed within 

 a crvstalline lorica. Amongst Confervas. 

 1-4600"; a tablet of 16, 1-570" in breadth. 



G. tranquillum. — Corpuscles green, 

 within a crystalline lorica, each 1-2880"; 

 a tablet of 16 corpuscles, from 1-140" to 

 1-220" in breadth. Tablet sometimes 

 tAvice as broad as long. 



G. hyakmwi. — Corpuscles transparent, 



