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SCIENCE 



[N. S. Vol. XXVII. No. 



of claws or clielse are alike and symmetrical, 

 but at about the fifth molt a transition from 

 symmetrical to asymmetrical differentiation 

 of the chelae normally occurs. The experi- 

 ments were planned to show to what extent 

 asynunetrical differentiation can be controlled 

 by the amputation of one chela, thus giving 

 the remaining chela the greater advantage 

 in growth. The results show (1) that up to 

 the fourth molt right or left asymmetry of 

 the chelse may be produced at the will of 

 the experimenter; (2) that during the fifth 

 stage (i. e., between the fourth and fifth molts) 

 experimental control ceases; and (3) that in 

 later stages of development, when the asym- 

 metry of the chelae has become established, the 

 amputation of one or both chelae does not 

 reverse the original asymmetry. It appears, 

 therefore, that the factors controlling asym- 

 metry become operative after hatching and 

 are correlated with conditions of growth. 

 The histological changes which occur at these 

 stages of growth and regeneration are being 

 studied. 



Mr. E. E. Scammon discussed the accessory 

 chromosome as a determinant of sex. He 

 showed original preparations of the male 

 germ cells of insects, similar to those which 

 led McClung to formulate his theory of the 

 accessory chromosome as a sex-determinant. 

 There were also exhibited several preparations 

 of orthopteran germ cells in which the acces- 

 sory forms part of a huge multiple chromo- 

 some. The behavior of the accessory in these 

 forms was discussed in the light of the recent 

 work of Wilson and others, and the relation 

 between the condition of the accessory chro- 

 mosome, in the Orthoptera and other insect 

 types was shown. 



Dr. F. W. Thyng described several models 

 of the pancreas in embryos of the eat, rabbit, 

 pig and man. In the embryos studied no 

 reason was found for subdividing the ventral 

 pancreas into independent right and left parts. 

 Attention was called to the marked differences 

 between the human pancreas and that of the 

 other animals studied. The pancreas of the 

 rabbit and pig usually encircles the portal 

 vein; frequently it does so in the eat, but, 

 apparently, no such occurrence has been re- 



corded in man. The probable manner of de- 

 velopment of the rare human anomaly in 

 which the pancreas surrounds the intestine, 

 was explained. In addition to the two human 

 embryos modeled, eighteen others were studied. 

 In all of these the dorsal pancreas joined the 

 intestine nearer the stomach than the common 

 bile duct, but in the other mammals this con- 

 dition was reversed. 



Professor F. T. Lewis, in describing the 

 intestinal diverticula of mammalian embryos, 

 cited Osier's tribute in 1881, to Meckel, who 

 wrote of diverticula in 1812. " In the Hand- 

 buch der pathologischen Anatomic the subject 

 is treated at great length and we have an 

 admirable example of the thoroughness with 

 which the older anatomists did their work. 

 No detail has escaped him, and I doubt if any 

 new point in structure or mode of develop- 

 ment has since been determined." Until re- 

 cently, however, the regular occurrence of 

 epithelial diverticula along the small intestine 

 of mammalian embryos has apparently been 

 overlooked. There may be as many as forty- 

 eight of these in a human embryo of 22 mm. 

 Usually they degenerate, but it is possible that 

 they may persist to form anomalous diver- 

 ticula in the adult. There is reason to believe 

 that elongated forms may become detached, 

 thus giving rise to mesenteric cysts. The 

 embryonic diverticula are discussed at length 

 in the current number of the Atnerican Jour- 

 nal of Anatomy (Vol. 7, pp. 505-519). 



Dr. John L. Bremer described aberrant 

 roots and branches of the abducent and hypo- 

 glossal nerves. In the interval along the ven- 

 tral portion of the medulla between the roots 

 of the abducent and hypoglossal nerves, nerve 

 roots are found in certain human embryos 

 from the fifth to the tenth week. Of these 

 roots there are two classes: one running ven- 

 trally, as though to join the hypoglossal or 

 abducent nerves, or to join the glossopharyn- 

 geal nerve, to which no ventral branch has 

 been recognized heretofore ; and the other class 

 running laterally, to pass just posterior to the 

 accessory nerve, or, if arising further forward, 

 to pass just posterior to the glossopharyngeal 

 nerve. Roots of this latter class, from their 



