716 



SCIENCE 



[N. S. Vol. XXIX. No. 748 



Morphology of the Sound-transmitting Apparatus 

 in the Amphibia: B. F. Kingsbubt and H. D. 

 Eeed, Cornell University. 



Study of serial sections and models of repre- 

 sentatives of eight families and seventeen genera 

 of tailed amphibia has shown that there are two 

 skeletal structures fitting in the fenestra vestibuli. 

 The first of these, which we designate as the 

 columella, is connected with the cephalic edge of 

 the fenestra when a connection exists between the 

 ear capsule and columella at all. It bears a more 

 or less well developed process primarily connected 

 with the squamosal bone in Neeturus, Proteus and 

 Cryptobranchus. In adult Ambystoma, Amphi- 

 uma and Siren there is a secondary connection 

 of this process with the quadrate. The second 

 element, which we designate as the operculum, has 

 no skeletal connections but affords attachment to 

 a muscle, the m. opercularis of Gaupp. When 

 attachment of this element to the ear capsule 

 occurs it is with the caudal margin of the fen- 

 estra. The cephalic end of the operculum is in- 

 cluded within the lips of the fenestra vestibuli 

 while in its caudal extent it protrudes. This is 

 the type found in Diemictylus and Triton. In the 

 larval Ambystoma, at transformation, the colu- 

 mella becomes incorporated with the ear capsule 

 while from the latter the operculum is cut out 

 essentially by an extension of the fenestra ves- 

 tibuli. In the adult of some forms, e. g., Diemic- 

 tylus and Triton, only the operculum is present 

 while in others, e. g., Ambystoma and Salaman- 

 dra, both elements are represented. In still other 

 forms such as Plethodon and Gyrinophilus both 

 columella and operculum seem to be present and 

 very closely associated, although the develop- 

 mental stages upon which the final explanation 

 of the morphologic relations depends have not yet 

 been examined. 



On the Effects of Centrifugal Force on the Devel- 

 opment of the Eggs of the Frog and Sea Urchin: 

 J. F. McClendon, University of Missouri. 

 The imsegmented egg of Rana pipiens subjected 

 to a centrifugal force ^2,771 X gravity for sev- 

 eral minutes, is separated into three layers as 

 follows: a centrifugal yolk layer containing the 

 black pigment granules, an intermediate proto- 

 plasmic layer (containing the nuclear elements) 

 and a centripetal fatty layer colored with yellow 

 pigment. Egg material was centrifuged in mass 

 and enough of each layer obtained for certain 

 chemical analyses. Morgan found in 1902 that a 

 certain amount of centrifuging prevented the cen- 



trifugal layer from developing. When subjected 

 to more centrifuging no part of the egg develops. 

 When the centrifuged egg partially develops, the 

 centripetal and intermediate layers are more or 

 less mixed in the early cleavage, so I have in the 

 following tables added together the analyses of 

 the centripetal and intermediate layers imder the 

 name of the former. Table I. gives the per cent, 

 of water (W.) and solids (S.) in the layers. 

 Table II. gives the per cent, of extracts (E.E. = 

 ether extract, A.E. ^alcohol extract, W.B. ^ 

 water extract) and residue (R.) in the solids. 

 Table III. gives the per cent, of phosphorus (P.) 

 in the extracts and residue. Cp. = centripetal 

 and Cf. = centrifugal layer. 



TABLE I. 



Layer W. 



Frog: Cp 74 



Cf 48 



Arbacia : Cp 88 



Cf 79 



TABLE II. 

 Layer E.E.-I-A,E. W.E. 



Frog: Cp 51 34 



Cf 30 10 



Arbacia: Cp 49 20 



Cf 38 10 



TABLE III. 



P. in p. in 



Layer E.E.+A.E. W.E. 



Frog: Cp 0.018 1.0 



Cf 0.54 1.2 



Arbacia: Cp 2.36 17.0 



Cf 2.74 13.0 



0.4 

 1.3 

 3.2 

 1.6 



In Tables I.-III. it is observed that there are 

 great differences between the composition of the 

 two layers, and this is correlated with their dif- 

 ferent capacity for development. 



If the egg of Arbacia be centrifuged it is sepa- 

 rated first into two and later into four layers. 

 By freezing and crushing the eggs and centri- 

 fuging in mass I obtained two layers correspond- 

 ing to the two first obtained in the entire egg. 

 Centrifugal force has little eflfect on the develop- 

 ment of the egg of Arbacia. By inspecting the 

 last two lines in Tables I.-III. it will be noticed 

 that there is very little difference between these 

 two layers in composition, and this is correlated 

 with the fact that there is little difference in their 

 capacity for development. 



Centrifugal force causes fiattening of the mitotic 



