On the present state of Zoology. 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 be 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,-]- 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 Rotatoria he has no- 

 ticed certain internal organs resembling branchise, 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. Journ. vol. xx. p. 42. 



