

588 CELL DIVISION IN EGGS OF CREPIDULA. 



Fig. 132. Exp. 875: Second polar spindle at animal pole; sperm nucleus has formed a spindle (cFSbV 

 the homogeneous chromatic sphere below this may represent an accessory sperm nucleus (d"iV). 



Fig. 133. Exp. 875: First cleavage spindle; the seven chromatic spheres may represent accessory 

 sperm nuclei (<?N). 



Fig. 134. Exp. 875: Enormous second polar body containing large nucleus and yolk; two nuclei and 

 accessory sperm nucleus ( o"iV) in egg. 



Fig. 135. Exp. 875: Probably J blastomere containing polyaster and with a micromere which has 

 just divided. 



Fig. 136. Exp. 872: Three blastomeres showing reversed polarity, the spheres, nuclei and cytoplasmic 

 areas lying at the pole opposite the polar bodies ; one sphere is found in each cell but in the two larger ones 

 the nuclei are multiple. 



Fig. 137. Exp. 875: Two macromeres, one containing a triaster, the other a tetraster; the two micro- 

 meres are normal except for their large size. 



Fig. 138. Exp. 875: Similar to the preceding. 



Fig. 139. Exp. 875: Side view of an egg similar to figs. 137, 138. 



Fig. 140. Exp. 875: Macromeres A and B have not divided and the chromosomes are irregularly 

 scattered in the spindle; macromeres C and D have divided normally giving rise to first and second micro- 

 meres and the first set are subdividing normally. 



Fig. 141. Exp. 859: Chromosomes were scattered along the spindle during the third cleavage and 

 have given rise to chromatic connections between daughter nuclei, which resemble amitoses. 



Fig. 142. Exp. 872: The micromeres are larger than usual (two of them contain yolk) and they have 



caused a separation of A, B, from C, D. 



Fig. 143. Exp. 872: The micromeres are larger than usual and contain yolk; the macromeres are 

 separated and one which has just divided (Y, Y) contains yolk but no cytoplasmic areas; the chromosomes 

 are here scattered along the spindle axis, thus forming a chromatic connection. 



Fig. 144. Exp. 875: f blastomeres, each of which has given rise to one micromere, which has sub- 

 divided; the macromeres contain spindles along which the chromosomes are scattered irregularly. 



PLATE LIV. 



Effects of Diluted Sea Water. 



In all experiments represented on this plate sea water was diluted with equal parts of distilled water. 

 Fig. 145. Exp. 858: Several micromeres have been formed but the yolk has not divided; three of the 

 cells contain several nuclei and spheres, the result probably of polyasters, and one contains a tetraster. 

 Fig. 146. Exp. 993 (1) : Similar to the preceding; the protoplasmic micromeres are partly constncted 



from the yolk. . w 



Fig. 147. Exp. 858: Exogastrula; similar to the preceding but of a more advanced stage; the multi- 

 nucleate yolk cell is uncovered by the ectoderm. 



Fig. 148. Exp. 993 : Similar to the preceding. , 



Fig. 149. Exp. 993: Side view of an egg placed in diluted sea water in the 2-cell stage; the second 

 cleavage of the yolk was suppressed, but several micromeres have been formed from each macromere. 



Fig. 150. Exp. 956: Egg similar to the preceding, viewed from the animal pole; each macromere 

 r>ntitflins a laro-P nnnHrinnrtitP niirieua and has triven rise to twelve micromeres, which cannot be lndiviau 



ally identified. 



Exp. 993 : Isolated i blastomere, the yolk cell has 



micromeres 



Figs. 152, 153. Exp. 858: Top and side views of eggs which were placed m diluted sea wdiei **«* 

 formation of the 1st set of micromeres; several dividing cells contain triasters or tetrasters and tne cnr ""V 

 somes are widely scattered; chromatic connections between daughter nuclei are falsely suggestive 



aim fIg." 154. Exp. 858: Side view of egg placed in diluted sea water after formation of the three : sets i oi 

 micromeres which are approximately normal; scattered chromosomes have given rise to cnromauo 



nections between daughter nuclei. i + q .+i,p macro 



Fig. 155. Exp. 993: Isolated f blastomeres which have produced a f micromere plate, tne 



mere AD has given off the mesentoblast 4d which is now dividing in normal manner. indicatec 



Fig. 156. Exp. 871: The 1st set of micromeres have divided twice in normal directions !L Hivisioi 

 by the arrows, giving rise to twelve micromeres ; in the formation of the 2d set of micromeres tne tu 



of the macromeres was approximately equal. . ■ , , ,„. nnrmallv 



Figs. 157, 158. Exp. 858: Eggs in which the nuclear division at the 2d c eavage took P ace nora^ 



three auartets of micromeres were formed 



normal 



m approximately normal manner, aitnougn mere are oniy wo sep»i»ie w*^"- — ^ 



cells 4d and 4c form simultaneously from the undivided macromere CD, thou g h A . m .J 10 ^^ 1 i°tase 

 mesentoblast) forms at the 24-cell stage, while 4c (an entoblast) does not form until tne w-ceu & 



