Making, again, all due allowance for the simplicity of the jaciors involved, a combina- 

 tion of similar characters in eggs establishes a presumption of phylogenetic relations in the 

 parents. 



The egg, although the product of an individual bird and susceptible to some degree of 

 modification by that parent, is, in its more fundamental characters, the embodiment of a 

 quasi-independent line of development, viz., the reproductive stream. 



The somatic significance of the individual is probably subordinate to and determined 

 by that of the reproductive stream. 



The rate of change in the evolution of the egg is neither determined by nor concomitant 

 with the rate of change in the evolution of the individual. 



The direction of change in the evolution of the egg is not largely, or perhaps not at all, 

 determined by the direction of change in the evolution of the individual. Being rather a 

 quasi-independent embodiment of the creative stream, it owes a part of its character to inde- 

 pendent environmental reaction. 



The egg being of much simpler function than the individual, the rate of change in the 

 egg is likely to be very much slower than that of the individual. This sometimes amounts to 

 practical stagnation, as in the eggs of the Hummingbirds ; and a comparatively slow rate is 

 characteristic of the eggs of all non-Passerine birds. In the eggs of Passerine birds only, 

 there is to be observed a notable quickening of the rate of evolutionary change, with a result- 

 ing variety and instability, affording in many instances evidence of changes actually in 

 progress. 



Because of this observed slow rate of change in the eggs of non-Passerine birds, the 

 evolution of tlie egg appears to lag behind that of the bird, and by so doing the egg often 

 preserves a record of phylogenetic history otherwise lost to our knowledge or powers of per- 

 ception. The evidential value of the egg, therefore, is of the highest significance in the 

 determination of the phylogenetic history and relations of non-Passerine birds. W here other 

 evidences fail, or are obscured, the evidence of the egg becomes of transcendent significance. 



The evidence of the egg so consistently supports and underwrites the sum of all other 

 evidences, where these are clear, that it may be unhesitatingly followed and be deemed de- 

 cisive, where other evidences are conflicting or obscure. 



In particular, and because of all the foregoing conclusions, groups apparently homo- 

 geneous in structure and only slightly different in appearance, are assuredly only remotely 

 related in time if their eggs snow decided differences. 



There is, of course, much more that might be said regarding the significance of 

 the egg as evidence, but the foregoing considerations are sufficient tor our approach 

 to the study ot the Alcitormes. in tne marked diversities ot the eggs, whicn serve 

 to throw tne Alcirormes into hve sharply-defined groups, we believe that we have 

 the key to the pnylogenetic appraisal ot this natural order. It is only in the light 

 of the egg that the history ot the group can be in any wise clearly understood, in 

 default 01 paieontological evidence (and that is neither clear nor copious), the 

 remarkable somatic Homogeneity ot this group might lead us to suppose it ot com- 

 paratively recent origin, say a Miocene offshoot 01 the L,aro-Eimicoiine stock. .But 

 tne oological evidence shows that a chasm yawns between the .flUhnaae (.the Auk- 

 lets proper and the Dovekie, as outlined below) on the one hand, and the four 

 remaining families, the Alcidae, the if raterculiaae, the Cepphidae and the Synth- 

 hborampnidae. A very considerable gulf probably separates tne iEtfninae from the 

 Allinae and the fissure between them may possibly reach back as far as that between 

 the two divisions above defined. These main lines will scarcely converge above the 

 upper Eocene, and 1 would sooner surmise the very lowest Eocene. 



That the various species of the Alciformes should have followed such closely 

 parallel lines of development is interesting, but in no wise exceptional. Like the 

 Penguins and the .Petrels, the Auks have been subjected throughout the icons of 

 geological history to fairly uniform conditions. Some movement to or from the 

 North Pole there has doubtless been in obedience to the great fluctuation of climate, 

 which we know to have occurred; and the actual divergence of species was doubt- 

 less accomplished when some vast glacial epoch, not the last, forced the birds south- 

 ward and apart. Even when a tropical climate prevailed in Greenland, the group 

 as a group might have been enjoying fairly uniform conditions in its circumpolar 

 habitat. That their lines of cleavage are very ancient we know from the indisputable 

 evidence of the egg. And we need not even predict any acceleration of the rate of 

 change in the evolution of the Alcine egg. The presumptions are all against it. The 

 eggs of the Spheniscidae, the Penguins, do not vary save in size and shape, as much 

 as do the eggs of Auklets and Dovekies, respectively. The eggs of the Procellarii- 

 formes, a most ancient order, offer only the feeblest variation in color, a tinge of 

 primitive red, repeated alike in Albatross and in Petrel but not in Shearwater; and 

 they offer only one (very dubious) departure from the singular number. Every 



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