During the sessions, the question of exactness in identifying and comparing homologues was discussed by several participants. Professor Butler stated that the thought held by some, that differences arise in going back along the jaw, might also be viewed alternatively to represent structures on anterior teeth as degenerate forms of those on the posterior ones. Patterson also thought that he could not place any great trust in premolar analogy and that, as he stated in the Brussels Conference in 1956, "it is a dangerous tool."Butler and others also questioned identification of cusps by their relationship to crests. Butler asked, "How sharp does a convex surface have to be before it becomes a crest? . . . On a photograph a highlight on a slope is difficult of identification . . . in some cases I would say that there is not a crest where one is claimed." He also went on to say that having crests running across a tooth in the upper and lower jaws does not make the crests homologous, "Nor does it make the cusps at their lingual ends homologous." -A.A.D.
Cohen and Berrill (1936) have given an interesting account of observations on eggs of Ascidiella aspcrsa and Phallusia rnainillata.After the jelly was digested by the gastric juice of the crab Munida, the eggs were stained in toto with a vital dye (particularly Nile-blue sulfate) and subsequent events studied with special reference to changes in the form of the germ and in the appearance of the vital dye within the egg.
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