Zoological Society. 57 



portant characteristic differences between all these animals, as have 

 hitherto been uniformly believed to exist. I refrain from proceeding 

 further in order not to overpass the boundaries of analogies and of 

 truth ; but it might happen that the objection proposed by Von Baer 

 should lead to this result ; not that the Monotremata should be thrown 

 back into the centre of the Mammalia, but that the Cetacea should 

 be separated from among them. The affinity of structure, if it be 

 such as the German physiologist announces, may lead to an idea 

 that the mode of nutrition which I have sketched for the Monotre- 

 mata may be equally adapted to the Cetacea. Formerly one mode 

 only was known, and it was supposed a priori that the Cetacea must 

 have passed through it. At all events it is necessary to revise the 

 doctrine of the nutrition of thejbetus of Cetacea. 



" Secondly, Mr. Owen points out the contradictoriness of my two 

 opinions in two papers published at an interval of less than a month, 

 and this is fair play in his capacity of critic. Nevertheless I had 

 scarcely touched on the fact relative to the egg-shells in my first 

 paper, proposing to return to it again. This I actually did some 

 weeks afterwards, when I conceived a system complete in itself, well 

 connected, opening out new views to research, and of which I frankly 

 declare that I had not the smallest idea a few days before I became 

 attached to it. Let it not, however, be believed that I present either 

 my old or my new conjectures as facts, the solidity of which I de- 

 cidedly maintain. In the absence of facts, I venture to recur to pre- 

 sumptions, which may become motives for research ; but if I calcu- 

 late certain probabilities, I merely desire to have applied to them 

 the criterion of observation. I know well that the mind of no man 

 is endowed with the faculty of imagining with regard to substantial 

 bodies, of distinctly conceiving the idea of a form. What has been 

 seen of this kind is "thenceforth known. Seriously admitting the truth 

 of this proposition, I merely wish to play a useful part, restricting 

 myself to the duties of a naturalist having the privilege of age, con- 

 fident in the experience of ancient studies, and acquainted with the 

 possible extent of the diversities of the acts of nature, in order to 

 assist observers less practised than myself in the study of natural 

 history, so that if there should exist in the most distant part of the 

 globe, organic conditions which we are interested in becoming im- 

 mediately acquainted with, I may say to them ' There is a chance 

 that it is A, or B, or C ; see what is the fact; instruct us with re- 

 gard to it.' 



" Thirdly, The monotrematic glands follow the phases of the de- 

 velopment of the sexual apparatus : like the mammary, they form 

 part of it, being large only in the females. To this I answer that it is 

 presuming too much with regard to the resources of nature, (which 

 shows on the contrary a tendency, as well as the most ingenious 

 means of execution, for a diversity of forms,) to fall into absolute 

 rules. What do we know of it? On the contrary, let us better un- 

 derstand our duties; let us constantly restrict ourselves to the con- 

 sideration of facts. It is a means of exposing ourselves to grave 

 mistakes, if we so easily and so precipitately determine with regard 



Third Series. Vol.4. No. l'J. Jan. 1 838. 



