178 



SCIENCE 



[N. S. Vol. XLIV. No. 1127 



itself has come to an end, but that the work 

 of the author is finished too. There are many 

 who can carry forward investigations and com- 

 plete new discoveries, but there are very few 

 who are made competent by their thorough 

 scholarship to understand, and through their 

 delightful style to explain, the evolution of 

 scientific thought from one age to another. 

 Percy M. Dawson 



SPECIAL ARTICLES 



THE PROCESS OF FEEDING IN THE OYSTER 



A valuable contribution to knowledge of the 

 ciliary mechanisms of Lamellibranch mollusks 

 has been made by James L. Kellogg in Vol. 26, 

 No. 4, of the Journal of Morphology. 



In this paper Dr. Kellogg brings together, 

 with numerous illustrations, his observations 

 on the ciliary tracts of structures found within 

 the mantle chamber of thirty-one species of 

 lamellibranchs. 



In each case the observations were made on 

 the animal after one of the valves of its shell 

 had been removed, and the presence and direc- 

 tion of ciliary currents were determined by 

 means of powdered carmine, fine black sand or 

 masses of diatoms, deposited upon the parts 

 under observation. 



Among the several conclusions at which Dr. 

 Kellogg arrives as a result of his study con- 

 cerning the activities and functions of these 

 tracts of cilia, the following, published on 

 pages 699 and 700, are those to which the " oral 

 exceptions," referred to by Dr. Kellogg on 

 page 640, have been taken and they are the 

 ones also which will be called in question in 

 this paper: 



1. Volume alone determines whether the collected 

 foreign matter that reaches the palps shall pro- 

 ceed to the mouth or shall be sent from the body 

 on outgoing tracts [of cilia]. 



2. A Lamellibranch is able to feed only when 

 waters are comparatively clear — when diatoms are 

 brought to the gill surfaces a few at a time. In 

 muddy waters, all suspended particles, of whatever 

 nature, are led to outgoing tracts. 



3. There is no selection or separation of food or- 

 ganisms from other water-borne particles. 



4. The direction of the beat of cilia is never 

 changed. 



The exceptions taken to these statements 

 were not based, as Dr. Kellogg states, on the 

 fact that the waters over Chesapeake oyster 

 beds are normally muddy for long periods of 

 time or upon the fact that the stomach con- 

 tents of oysters always contain a larger volume 

 of sand than of food organisms, although both 

 of these facts are difficult to explain on the 

 Kellogg theory, but they are based primarily 

 upon the results of experiments, to be described 

 later, which show that oysters can and do feed 

 rapidly and continuously in waters that are 

 turbid with sediment. 



Before passing to a consideration of the re- 

 sults of these experiments, however, which bear 

 directly upon the first and second only of Dr. 

 Kellogg's conclusions (as numbered in this 

 paper), reference may be made to the findings 

 of other observers not in agreement with those 

 of Dr. Kellogg, which indicate that the con- 

 clusions numbered (3) and (4) were possibly 

 drawn from an insufficient basis of observation 

 or that the methods of study employed by Dr. 

 Kellogg were not designed to reveal all of the 

 activities, of the ciliary mechanisms of lamelli- 

 branchs. 



REVERSAL OF CILIA AND FOOD SELECTION 



In Stentor, Schaeffer 1 has shown that there 

 is a selection of food particles brought about 

 by changes in the beat of the cilia of the pouch 

 and funnel, certain particles being rejected by 

 a localized reversal of the cilia. He also found 

 that the behavior of the animal toward food is 

 not the same when it is in a condition of 

 hunger as when in a condition of satiety. 



Stentor is not an isolated example of proto- 

 zoan possessing the power of food selection and 

 rejection exercised through the control of the 

 ciliary mechanism of the mouth region. Nu- 

 merous other cases might be cited. 



Cases of reversal of cilia are also reported 

 among metazoan animals, Parker 2 having 

 found that in Metridium the cilia on the lips, 

 which normally beat outward, can be made to 



i Asa Arthur Schaeffer, ' ' Selection of Food in 

 Stentor cceruleus," Jour. Exp. Zool., 1910. 



s G. H. Parker, ' ' The Reversal of Ciliary Move- 

 ments in Metazoans, " Am. Jour, of Physiology, 

 Vol. XIII., 1905. 



