106 Reviews and Records in Anatomy and Physiology. 
Ehrenberg. Examined with the highest and best microscopic 
powers, they are found to be composed of a more or less globular 
head to which is attached a thread-like tail of considerable length. 
This head taken by itself has all the appearances of a simple cell, 
——it is nucleated and even nucleolated ; yet the whole body moves 
about by means of its tail in a most animal-like manner and it 
studying the field one can hardly divest the mind from the opin- 
ion that they are true animals. 
The intestinal canal of many insects likewise, especially those 
feeding in damp, moist places, will often be found teeming with 
forms so large and numerous that it is singular that the insect 
should live. Many of these forms are composed of a more of 
less globular sac filled with a punctiform matter in which lies 4 
round nucleus; at one extremity of this sac is an orifice surround 
ed by a circle of cilia. Others are more vermiform, regularly 
wrinkled, but apparently non-nucleated. These belong to the 
Gregarine, and are the forms upon which Siebold and Kolliker 
ave based their doctrine of unicellular animals. Other instances 
might be cited, equally prominent, which almost daily come ut 
der the eye of the microscopist in his studies in the lower depatt- 
ment of the animal kingdom. bch 
Our own observations upon these objects have not led us to the 
view that they are, any of them, perfect individual forms ;* on the 
other hand, research is constantly reducing their generic numbers, — 
on the one side, by showing that many so-called genera are only 
different developments of one and the same form; and by remov- 
ing them, on the other, from that Receptaculum omnium anima- 
* 
recent investigations of Siebold and others, in Helminthology, 
sh 
Gregarine, or other forms which have been grouped under special 
genera or species, we must wait further research, and they will 
n 
valid; and some of those which in late years have been regarded 
as among the most constant, have quite recently been declared 
equally unsound. . 
+ Thus Agassiz bas shown that Paramecium and Bursaria, de. are only larvel 
forms Annals of Nat. Hist, vi, 1860, p.156. uglena, Amabs 
others, will most probably meet with a like resolution. 
