118 DESCRIPTION OF [Polygastrica. 



inflected light) at the base of the proboscides has been per- 

 ceived by Ehrenberg, which he conceives to be the mouth. 

 75. GONIUM pectorale (M). The breast-plate Gonium. 

 The form of this animalcule, or more correctly, cluster 

 of animalcules, is shewn at figs. 38, 40, and 41. It consists 

 of sixteen spherical bodies, enclosed within a transparent 

 lorica or shell, and disposed regularly in a quadrangular 

 form, like the jewels in the breast-plate of the Jewish 

 High Priest. They are all arranged in the same plane. 

 The four centre ones are generally larger than those which 

 surround them, and the diameters of the three smaller 

 balls are about equal to the two larger centre ones to 

 which they are attached ; the external corners are con- 

 sequently vacant. As these animalcules swim and revolve 

 in the water, they occasionally present a side view to the 

 observer, when the circumference of the larger central 

 globules may be seen projecting beyond the others. 

 Sometimes the cluster appears irregular; this happens 

 when the larger animalcules have arrived at maturity, and 

 some of them are separated from the cluster. When they 

 are all of equal diameters, the group divides across the 

 middle, both vertically and horizontally, and separates into 

 four clusters, each consisting of four animalcules. As 

 soon as a cluster has separated, the respective animalcules 

 increase in size, and in a short time their surfaces appear 

 decussated, and they severally begin to form into regular 

 clusters, like the original one to which they belonged. 

 They are of a beautiful transparent green colour, and in 

 swimming, the globules often appear of an ellipsoidal 

 figure (see fig. 40); their forms, when viewed under the 

 microscope in the usual way, are so simple, and so different 



