On the present state of Zooloyy. 9 
different degrees of complexity of structure ; and that while some are 
true Polypi, others are more nearly allied to the compound Ascidice.* 
Indeed it may he observed generally, that the lower we descend the 
scale of organization, the less reliance are we able to place upon mere 
external characters, and the more it becomes necessary to investigate 
those derived from anatomical researches. 
Did our limits allow, we should here proceed to notice the most 
recent additions which have been made to our knowledge of animal 
organization. We might pursue the subject through each department 
of the science, and show the endeavours which were being made to 
advance its progress, as connected with the two principles above al- 
luded to. But we can scarcely do more than make a few general re- 
marks on this head, referring for illustration to the more important 
instances. And first, we are called upon to notice the increased at- 
tention paid at the present day to the structure of the more minute 
and delicately-formed animals ; and the discovery, uniformly follow- 
ing, that this structure is not by any means so simple as was gene- 
rally supposed formerly. This remark bears especially upon the In- 
fusoria which have been so profoundly studied by Professor Ehren- 
berg. We need not speak of the first two memoirs by that acute 
observer on these animals, which are probably well known to all our 
naturalists. We may, however, allude to a third, published more 
recently,f in which he announces the existence of several systems of 
organs which he had not previously detected in this group. Thus he 
has discovered in the Polygastrica a pharynx and teeth, the absence 
of which- he had formerly considered as a distinctive character of that 
division. He has also observed what he is inclined to regard as male 
sexual organs, and likewise a gland secreting a deep blue-coloured li- 
quid supposed to be the pancreatic fluid. In the JRotatoria he has no- 
ticed certain internal organs resembling branchiae, and, what is a yet 
more important step, apparently distinct traces of a nervous system. 
It is curious to reflect, as Ehrenberg himself observes, with reference 
to the combined discoveries announced in this and in his two former 
memoirs, that he has been thus led successively to detect in the smal- 
lest animals which can be perceived with the assistance of the micro- 
scope, all the systems of organs which form the essential part of the 
human structure ; and that these organs are not rudimentary, but, 
after their kind, as perfect as they are in man, It would seem as if 
* Ann. des Sci. Nat. torn. xv. p. 5. 
f An abstract of this memoir will be found translated into French, in the 
Ann. des Sci. Nat. (Second Series.) torn. iii. pp. 281 and 363; and into En- 
glish, in the Edin. New Phil. Jourii. vol. xx. p. 42. 
