Helen Dean King

THE FORMATION OF THE NOTOCHORD IN THE AMPHIBIA

A study of the mode of development of the notochord in the common toad, Bufo lentiginosus, and of the frog, Rana palustris, has brought to light certain points that have a bearing on the formation of the same structure in related groups. A vast amount of work has already been done along this line, yet a wide difference of opinion exists among embryologists regarding the origin of the notochord in the Amphibia. It is hoped that the results recorded in the present paper may help to clear up this question. The material used was fixed in corrosive-acetic (5? glacial acetic acid), and the sections were stained on the slide with a mixture of borax-carmine and Lyons blue as described in a previous paper (King, I I). This stain gives particularly good results when it is used on freshly preserved material, as then all of the nuclei become dark red, the ectoderm and mesoderm appear dark blue, while the yolk cells take but a pale blue tint and, therefore, are easily distinguished from the other cells. This sharp definition of the tissues was of great assistance, particularly in the study of the sections of Bufo. All of the drawings given in the present paper were outlined with the aid of a camera lucida.

THE FORMATION OF THE FIRST POLAR SPINDLE IN THE EGG OF BUFO LENTIGINOSUS

In a previous paper on “? The Maturation and Fertilization of the Egg of Bufo lentzA§inosus―(King, io), the formation of the first polar spindle and the subsequent divisions of the chromo somes were very incompletely described owing to a lack of ma terial showing the details of these processes. During the spring of 1899, a large number of toads were collected soon after they had emerged from their hibernation, and from three of them suf ficient material was obtained to give a more complete history of the late maturation processes. A short account of my study of this period in the development of the egg has already appeared