ORGANIZATION AND CELL-LINEAGE OF ASCIDIAN EGG. 1 
In the face of all this antecedent work, it may seem superfluous to devote yet 
another paper to this subject, and nothing was further from my purpose when 1 
began. It was in the attempt to find out the manner in which the ascidian egg 
comes to form its polar bodies at the endodermal pole, as described by Castle, that I 
was led to conclusions radically different from his, as will be described later, and this 
induced me to make a detailed study of the cell-lineage of three different genera of 
simple ascidians. In such a field it may be expecting too much to hope that my 
observations will meet with general acceptance; but perhaps it may be proper for 
me to say that I have spared no pains or labor to make them accurate. 
C. MATERIAL AND Metnops.—Early in July, 1903, while working at the Marine 
Biological Laboratory, Woods Holl, Mass., I began the study of the maturation 
and fertilization of the egg of Crona intestinalis (L.) Flemming, with the aim men- 
tioned in the preceding paragraph. Only a small number of these animals was to 
be found at that time at Woods Holl, though they occurred more abundantly later 
in the summer. I therefore turned my attention to two other simple ascidians, 
Molgula manhattensis Verrill and Cynthia (Styela) partita Stimpson, both of which 
occur in considerable numbers іп the Woods Holl region. The very first lot of the 
living eggs of Cyz/hza which I examined showed a most remarkable phenomenon 
and one which modified the whole course and purpose of my work; for there on 
many of the unsegmented eggs, whieh were of a slate-gray color, was a brilliant 
orange-yellow spot, which in other eggs appeared in the form of a crescent or band. 
Further observation showed that this crescent became divided into two equal parts 
at the first cleavage and that it could be followed through the later cleavages and 
even into the tadpole stage. I thereafter, for a considerable portion of the summer, 
devoted myself to the study of the living eggs of Cy»s/A7a, and a record of these 
observations will be found in the body of this work and in plates I-V. Afterward 
I took up also the living eggs of Crona and Molgula, and finally I fixed and pre- 
pared for microscopical examination, both as whole objects and as serial sections, 
the eggs and embryos of all three of these genera. 
Castle (1896) has described in considerable detail the time and manner of egg 
laying in these three genera, and his observations I can entirely confirm. Тһе eggs 
of Ciona and Molgula are laid in the early morning, a little before daybreak, while 
those of Cynthia are laid in the late afternoon, a little before sunset. These 
ascidians rarely lay eggs the first day they are in the laboratory. Since the 
yellow pigment of the egg of Cynthia is difficult to observe by artificial light, it 
was necessary to take eggs from the ovary or oviducts and artifically fertilize 
them in the morning in order to be able to study by daylight the later stages in the 
development. А large proportion of such eggs never develop, though the. eggs 
seem ripe and the spermatozoa are active; however, some of them develop into 
normal embryos and tadpoles, and from such I have obtained material for the study 
of the later stages of the living egg. Whenever possible, however, I have relied 
upon eggs which were normally laid and fertilized, inasmuch as all such develop 
normally. In Суола and Molgula it is very easy to artificially fertilize the eggs; 
