ZOOLOGY AND BOTANY, MICROSCOPY, ETC. t 511 



Proteus, llenooranchus, Menqwma, Siredon, Cryptobranchus, Amphiuma, 

 Siren, and Ellipsoglossa. He gives a summary of his morphological 

 results, as well as a detailed account of the various forms. 



Development of Mesonephros and Miillerian Ducts inBAmphibia.* 

 R. W. Hall has investigated these in Amblystoma, Rana and Hyla. In 

 Ambly stoma the mesonephric blastula is derived from a portion of the 

 somite which is homologous with the mesomer of elasmobranchs, and it 

 contains both splanchnoderm and somatoderm. The more anterior 

 blastulse probably never lose their connection with the two layers of the 

 lateral mesoderm. The outer tubules (at least in the anterior primary 

 units) therefore contain both somatoderm and splanchnoderm. The 

 morphologically dorsal angle of the body-cavity is not at the upper limit 

 of the mesentery, but lies just mesial to the AVolffian duct. Hence the 

 germ cells (except in very early stages) all lie in the splanchnoderm. 

 The secondary character of the dysmetamerism of the urodele shows 

 itself in the fact that the primary blastulge can be divided into two sets, 

 in one of which the elements (those of the " first order ") are meta- 

 merically arranged. It is suggested that the units of the "second order" 

 represent the final product of a phylogenetic evolution in which a number 

 of secondary units have been transformed into primary ones. Tertiary 

 sets arise from secondary, and quaternary from tertiary, etc. At the 

 period of metamorphosis only primary and secondary units'] have- pro- 

 duced outer tubules, and in all probability the outer tubules are con- 

 lined to these two sets of units throughout life. The development of 

 the Miillerian ducts is followed in great detail. At one point it fuses 

 with the Wolffian duct, and then grows backward free. That the 

 Wolffian duct contributes cells helping to form the Miillerian duct in 

 this region seems almost beyond question. The greater part, however, 

 — throughout the entire extent of the mesonephros — grows back in- 

 dependent of the Wolffian duct. The results of similar observations 

 on Rana and Hyla are included in the paper. 



Development of Layers and Organs in the Terminal Bud and Tail 

 of Teleost Embryos. \ — A. Swaen and A. Brachet have studied the 

 development of the caudal region in Triittafario, Leuciscus cephalus and 

 Exococtus volitans. The first chapter discusses the development and 

 growth of the trunk at the expense of the terminal bud ; the second is 

 devoted to the development and elongation of the tail ; the third de- 

 scribes the completion of the posterior extremity, and the formation of 

 the anal plate. 



Development of Pancreas, Liver and Spleen in the Sturgeon. J— 

 A. Nicolas has studied the development of these organs in Acipenser 

 ruthenus. He finds that the dorsal primordium of the pancreas is 

 single ; it is formed by the constricting off of a groove, which becomes 

 a tubular diverticulum, from the region giving rise to stomach and 

 duodenum. There is nothing peculiar except its primitive situation, 



* Bull. Mus. Zool. Harvard, xlv. (1904) pp. 31-125 (8 pls.).| 

 t Arch. Biol. xx. (1904) pp. 461-610 (4 pis.). 

 % Tom. cit., pp. 425-60 (3 pis.). 



