396 EDWIN G. CONKLIN 



as in Cynthia and Ciona. If eggs are fixed in Kleinenberg's 

 picro-sulphuric mixture, and are then stained in a dilute solution 

 of haematoxylin, in the manner described by me in former 

 papers (1897-1905), it is possible to follow the cell-lineage of 

 Phallusia to an advanced stage; in such study it is easy to see 

 that the position and order of the cleavage planes, and the form 

 and constitution of the resulting blastomeres are typically like 

 those of other ascidians. This is true not only of the main features 

 but also of every detail of the cleavage, such as the position and 

 direction of the cleavage planes and pressure surfaces, and the 

 relative quantities and positions of yolk, cytoplasm and nuclei, 

 mesoplasm and chorda-neuroplasm in various blastomeres. In 

 all of these details of egg organization, before and during cleavage, 

 the eggs of Phallusia are almost precisely like those of other 

 ascidians. On the other hand the distinction between the va- 

 rious ooplasmic substances, such as ectoplasm, endoplasm, meso- 

 plasm, etc., are not so easily seen in Phallusia as in Cynthia and 

 it is doubtful whether they would have attracted my attention 

 if I had not been acquainted already with ascidian eggs in which 

 these distinctions are strikingly evident; this is true of fixed and 

 stained material as well as of the living eggs. In short Phal- 

 lusia is not so favorably a form for the study of egg organization as 

 is Cynthia ; nevertheless eggs of Phallusia which have been care- 

 fully fixed and stained show these ooplasmic substances in the 

 same relative positions and proportions as do the eggs of Cynthia. 

 The apparent homogeneity of the living eggs of Phallusia is 

 only apparent, not real, and is principally due to the absence of 

 pigment. Incidentally this shows, what I have emphasized 

 elsewhere, that the pigment of the ascidian egg is not an essential 

 or formative part of the ooplasm and that the region in which 

 pigment becomes localized, when it is present, differs from other 

 regions in more important respects than in the presence or 

 absence of pigment. In other words the localization of pigment 

 in such an egg as that of Cynthia is the result and not the cause 

 of ooplasmic differentiation and localization. 



The cup-shaped gastrulae of Phallusia, Cynthia and Ciona 

 are composed of identically similar cells — similar in lineage, 



