. Carnegie Institution of Washington publication. 18 Papers from the Department of Marine Biology. So far as my own experience goes there is no sign of any organ which can be called a testis nor of spermatozoa wandering through the tissues. I think that probably Thompsonia is to be placed with Sylon and Mycetomorpha as Rhizocephala which have substituted partheno- genesis for hermaphroditism. Coutiere also seems to refer to this organ in speaking of a distally situated growing point. I must confess myself unable to understand a good deal of his description without the aid of figures. His conce
. Carnegie Institution of Washington publication. 18 Papers from the Department of Marine Biology. So far as my own experience goes there is no sign of any organ which can be called a testis nor of spermatozoa wandering through the tissues. I think that probably Thompsonia is to be placed with Sylon and Mycetomorpha as Rhizocephala which have substituted partheno- genesis for hermaphroditism. Coutiere also seems to refer to this organ in speaking of a distally situated growing point. I must confess myself unable to understand a good deal of his description without the aid of figures. His conception of the life-history of Thompsonia, moreover, leads him to see in the visceral mass the abdomen of the Cypris larva and explain the prolifer- ation here by the laws of growth observed in Annelids and Crustacean larvae. DEVELOPMENT. The account which I give of the development of Thompsonia is very incomplete, for the material in my possession illustrates only a number of isolated stages. I have not been able to gather any information about the maturation of the A. Young egg cell. B. Oocyte nucleus has come to lie excen- trically owing to the development of yolk (in black globules). Four-cell stage: two micromeres (unshaded) and two macromeres (shaded) containing the yolk. FIG. 9.—Developing eggs of Thompsonia. X1000. D. Beginning of gastrulation; micromeres have C. divided; macromeres undivided. E. Development of gastrulation; appearance of vacuoles in the protoplasm of the macro- meres. F. Gastrulation complete; macromeres have divided once, so there are now four cells; more generally there seem to be three. In the youngest external sacs the visceral mass is occupied by small cells of uniform size. Amongst these there soon become differentiated young oogonia which are rather larger than the remaining interstitial. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of
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