Mechanics of feeding in the Mallard ( Anas platyrhynchos L

Mechanics of feeding in the Mallard (Anas platyrhynchos L.; Aves, Anseriformes).--G. A. Zweers, A. F. C. Gerritsen, and P. J. van Kranenburg-Voogd. 1977. Contributions to Vertebrate Evolution, vol. $. vii + 109 pp., 20 figures. Paper $19.75.--For many years, primarily since the 1920's and 1950's, arian morphology has progressively become less descriptive and more functional in its approach. Emphasis has shifted from asking what structure is present and the form it may take to discovering how that structure works. An attempt to construct a general historical overview of this change might recognize three main phases. First, there was an extension of the older descriptive work in which function was inferred from gross structure. In bone-muscle systems this procedure focused on the origins and insertions of muscles and the general configuration of joints. Statements were expressed in terms of the probable role that individual muscles played in moving bones from one position to another. This "phase" has continued up to the present and many published papers, Ph.D. theses, and the like have adopted this approach, although this type of analysis has lost its significance in the eyes of most functional morphologists. The second "phase," although present in some early papers, is basically a child of the 1960's. Investigators began to incorporate evidence from physiological studies in their analyses. The latter were not themselves physiological in approach; instead, muscles were analysed in more detail, their fiber architecture was noted, as was relative muscle weight and in some cases their fiber types, and then these data were interpreted using known (or surmised) physiological information to yield more precise functional statements about the movements of bone-muscle systems. This second phase allowed for a sense of increased understanding of these systems since one could now make inferences about relative muscle force, speed of contraction, length of shortening or stretching, and perhaps some statement about fatiguability. Yet the specimens being observed were quite dead, sometimes for years, and thus functional inferences remained conjectural. Finally, a third phase has begun to develop in the 1970's. It has now become fashionable within vertebrate functional morphology to perform physiological experiments on living organisms in order to discover what "really" is happening: inference, some workers would have us believe, has been virtually eliminated. Clearly, the third phase represents an advance in our knowledge and does not merely serve only as a showcase for elegant experimentation. Within arian functional morphology--excluding much fine work by physiologists themselves--this approach is uncommon, especially as it is applied to bonemuscle systems. Unquestionably, the finest work of its kind--perhaps in all the vertebrate literature• has been performed recently by G. A. Zweers and his colleagues in Leiden. Two studies have been published, both on the Mallard. The first (1974. Structure, movement, and myography of the feeding apparatus of the Mallard (Arias platyrhynchos L.). Netherlands J. Zool. 24: 323467) was concerned primarily with a functional analysis of the jaw and tongue apparatus. The second, under review here, was a follow-up study and details the role of the beak and tongue during feeding. In order to convey fully the importance of these studies it is necessary to consider both of them in this review.