MOEPHOLO&T OF OPISTHOCOMUS GEISTATUS. 81 



a sort of rough scaffolding, and not a Temple of Nature ; moreover, each ornithological 

 artisan will use his own classification, and that of no one else ; thus there are as many 

 systems as there are Ornithologists. We see this most instructively in the case of that 

 most skilful worker, whose classification I have just reviewed. In his Coracomorphse 

 six thousand species are fagoted together ; his Heteromorphse contains only one 

 species — Opistkocomus cristatus. It is true, however, that this bird differs more from 

 any other existing type than any, the most diverging, do amongst the whole multitude 

 of Passerines. Again, by choosing those characters in the members of two distant 

 Families that agree, and forgetting those in which they differ, it is not difficult to make 

 a " happy family " out of very discordant members. If we are desiring to use a compre- 

 hensive term, well and good ; but the binder round such a group should be made of an 

 elastic withy, and not of cast iron. Now in Prof. Huxley's Cecomorphse {op. cit. 

 pp. 457, 458), the Gulls, Petrels, and Auks are put together ; but the Penguins are 

 left out, and the term Spheniscomorphse merely means the same as Spheniscidse. But 

 the Great Auk was a very accurate isomorph of a Penguin. The extinct toothed birds, 

 ITesperornis and Ichthyornis, have to be packed together inside this Cecomorphous 

 bundle ; for the former is the quasi-parental form of the Grebes and Loons, and the 

 latter is the Gull of an old dispensation. The problem is rendered more difficult by the 

 fact that the Grebes, Loons, and Petrels, like the ancient Hesperornis, have the newest 

 form of avian vertebral articulation. Their cervical and dorsal vertebrae are cylindroidal 

 or heteromorphous ; whilst the dorsals in Gulls and the Alcidae are opisthoccelous. In 

 the Gulls, most instructively, there is a partial retention of the amphiccelous condition, 

 which is seen in the presacrals, generally, of Ichthyornis. Now as to Opisthocomus, 

 I would drop its group term Heteromorphse, and yet hold on to the spirit of that 

 term, whilst I discard the letter. This bird, an archaic Fowl, or Gallinaceous type, 

 differs from the Gallinaceous birds of its own Neotropical Territory, namely the 

 Cracidae, as much as the most Passerine of the Coccygomorphse do from their nearest 

 allies in the great Passerine group. This bird, like the Tinamous, belongs to the same 

 general stratum of old forms as the Ratitse ; but it has not, nor have the Tinamous, lost 

 the sternal keel, nor the size and strength of the wings. 



Its isolation suggests at once its ancientness ; its morphology, which throws some 

 light on its ontogeny, teaches the same thing. Like the Tinamou, it is an arrested 

 type ; the Eatitse are both an arrested and a degraded group. I suspect that the 

 earliest birds were Carinatse. 



b. The Light cast upon the Ontogeny of Birds by the Morphology of Opisthocomus. 



In the skull of Opisthocomus we have the fundamental form of that of a Carinate bird ; 

 it has undergone that remarkable change by which the upper face can be moved upon 

 the frontal region. In this it is above the Struthionidse, which, like Eeptiles, have no 

 such hinge. Its basipterygoids, although they die out, are truly Struthious. The 



