480 ARKIV FÖR ZOOLOGI. BÄNT) 1. 



distinct in different genera and species. In some systematic 

 works these pieces have even received special technical na- 

 mes as »cnlminicorn», »latericorn» etc. As far as I have been 

 abie to find ont in the to me accessible literatnre the homo- 

 logy of these pieces has not, however, been made out, the 

 anthors having in most cases confined themselves to the 

 simple statement »rhamphotheca componnd» or something like 

 that. In his extensive work »Yögel» in »Bronn's Klassen nnd 

 Ordnnngen des Thierreichs» (Systemat. Theil. Leipzig 1893) 

 Dr. Gadow writes as follows »Complicirte Schnabelscheiden 

 möchte ich als primär anffassen, wenigstens bei Ratitse, Cryp- 

 tnri, Steganopodes, Tnbinares, Sphenisci.» — — — — — 

 »Greneralisiren lässt sich hier schwer; es ist aber doch mög- 

 lich, in manchen Fallen anscheinend ganz verschiedene Schnä- 

 bel anf denselben Grnndtypus znriick zn fiihren, z. B. den 

 Schnabeliiberzug der Falconiforines anf den der Ciconiiform.es.» 

 Bnt that is all, and nothing is said abont possible homolo- 

 gies; for that the bill of one gronp of birds contains elements 

 homologons to these in the bill of others does not connt, 

 becanse it is axiomatic. It is therefore an attempt at a 

 more far-reaching homologisation that I shall try to set forth 

 in the following commnnication. 



It is generally accepted that the birds have been deve- 

 loped from a reptilian ancestry, which may have had some 

 affinity with Proganosauria and Binosauria and in any case 

 mnst have belonged to the series or snbclass for which H. F. 

 Osborn recently 1 has proposed the name Biapsida. To this 

 snbclass belong of recent animals Sphenodon, Squamata (in- 

 clnding lizards and snakes) and Crocodilia. It is of conrse 

 impossible to tell now with certainty in which manner the 

 horny shields of the head of the extinct Biapsida were arran- 

 ged. Bnt if some featnres of arrangement are common to 

 all different recent forms it may be assnmed with some 

 rather high degree of probability that they also were cha- 

 racteristic of the extinct members of the same snbclass. It 

 mnst be assumed as axiomatic that the skin of all terrestrial 

 reptiles was protected by a horny layer and this mnst for 

 the sake of mobility or other reasons be snbdivided or diffe- 

 rentiated in smaller or larger shields, plates or even gra- 



»Science». N. S. Vol. XVII. N:o 424. 1903. 



