Febkuaey 18, 1898.] 



SCIENCE. 



221 



row of large cells lying in the wall of the 

 body and extending along the mid- dorsal 

 line from the base of the stalk to the vicin- 

 ity of the arms. A second but not invari- 

 able characteristic is the presence of one or 

 miore flask-shaped organs attached to the 

 wall of the body near the basal end of the 

 stomach and projecting slightly forward. 

 The third characteristic is a modification of 

 the epithelial wall of the vestibule shown 

 by those individuals which have developing 

 larvae, and consisting in part of irregular, 

 tongue-shaped projections, whose free ends 

 may be invaginated and filled with a yolk- 

 like material. This substance may float 

 out into the vestibule. The modified epi- 

 thelium, as well as this yolk-like substance, 

 forms a source of food for the developing 

 larvae. 



Pleurivalent Spermatids and Giant Spermatosoa 

 and their Relation to the Centrosome Ques- 

 tion. F. C. Paulmier. (Presented by 

 E. B. Wilson.) 



Among the spermatids in Anasa tristis oc 

 casionally occur those whose nuclei are 

 double or quadruple the usual size, the 

 cell body being correspondingly enlarged. 

 "While otherwise normal, the double ones 

 have two centrosomes and two axial filia- 

 ments. 



These giant spermatids are due, the dou- 

 ble ones to the non-completion of the second 

 spermatocyte division, the quadruple ones 

 to the non- completion of both divisions. 



In the normal univalent spermatid the 

 single centrosome persistent throughout the 

 period of spermatocyte growth and division 

 apparently disappears and comes into view 

 later upon the other side of the nucleus. 

 Is this disappearence real or only ap- 

 parent ? 



In the bivalent spermatids the two cen- 

 trosomes of the second division apparently 

 disappear and two reappear at a later stage 

 in the Nebenkern. In the quadrivalent 



ones the four centrosomes of the first divi- 

 sion (the original two having divided early 

 in preparation for the second division) ap- 

 parently disappear, and later four appear in 

 the Nebenkern. 



This fact that the same number of cen- 

 trosomes which disappear —namely, two or 

 four — always reappear seems to prove that 

 the disappearance is only apparent and in- 

 dicates that the centrosome persists in some 

 form, perhaps hidden by the chromatin. 



The Maturation of the Egg under Different 



Conditions. A. D. Mead. 



The behavior of the Chjetopterus ovum 

 when subjected to different conditions shows 

 that many of the phenomena of maturation 

 and karyokinesis, which usually appear to 

 be correlated with one another, are in reality 

 independent. 



When the egg is allowed to remain un- 

 fertilized in normal sea-water the matura- 

 tion proceeds only as far as the metaphase 

 of the first spindle. When, however, the 

 egg is (a) fertilized with one spermatozoon, 

 (6) fertilized with several spermatozoa, or 

 (c) placed unfertilized in a solution of 

 potassium chloride, the polar globules are 

 extruded in a perfectly regular and uniform 

 manner, and certain characteristic changes 

 in the contour of the egg take place in all. 



Although these phenomena are the same, 

 the appearance of the greater part of the 

 cytoplasm of the egg is widely different in 

 the various cases. To illustrate : The for- 

 mation of the second polar globule, the re- 

 constitution of the egg-nucleus and its 

 migration toward the egg center, occurs in 

 the same manner whether (a) the egg con- 

 tains a sperm-nucleus and one huge sperm- 

 amphiaster, whether (6) it contains a 

 number of sperm-nuclei and sperm-amphi- 

 asters, or whether (c) it contains no sperm- 

 nucleus or radiation in the cytoplasm. 



Some Activities of the Polar Bodies in Cere- 

 hratulus. E. A. Andrews. 



