88 C. 0. Whìtman 



Fig. 94. The axial cell of a fiilly developed embryo (.15 mm long), showing two 

 germ-cells that have arisen by clivision of the posterior primary germ- 

 cell, and the anterior germ-cell still undivided. Osmic acid. 

 Fig. 95. From an embryo found free, in which the anterior primary germ-cell has 

 been replaced by two cells. The fact that the primary cells do not divide 

 simultaneously is to be connected with the fact that they do not originate 

 at the Same time. The first to arise is the first to divide. In figs. 90, 98, 

 the germ-cells behind the central nucleus [ne) take the lead in dividing. 

 This alternation of division between the two primary germ-cells (and 

 their products) has been offen observed. Osmic acid. 

 Fig. 90. The central portion of the axial cell of an embryo Dicyemennea Eledones 

 still within the parent. Length .15 mm. One of the two cells behind the 

 nucleus [ne] has divided. There is a considerable pause after each divis- 

 ion , during which the division-products grow to the size of the original 

 cell, similarly as in cleavage. Acetic acid. 

 Fig. 97. Central portion of a young Z)«oye/«n ?;iacrocep7io/t<?» (.■25 mm long). Here 

 are seen two pairs of small germ-cells, and, in front of each pair, a 

 single larger germ-cell. These pairs bave evidently arisen by the divis- 

 ion of germ-cells of the larger kind. Osmic acid. 

 Fig. 98. A somewhat less advanced condition of a still unliberated embryo. 



Acetic acid. 

 Fig. 99. Entire Contents of the axial cell of a young Bicyema tnmcutmn from 



Rossia. Length .3 mm. Acetic acid. 

 Fig. 100. The axial cell and contents of a young individuai .3 mm long. Acetic 



acid. 

 Fig. 101. The axial cell and its contents at a later stage {Dicyemennea Eledones). 

 Length .75 mm. Shows the arrangement of the germ-cells in a primary 

 Nematogen. Acetic acid. 

 Fig. 102. Aportion of a primary Nematogen, showing the central nucleus (we) and 



the scattered germ-cells [vg). Acetic acid. 

 Fig. 103. Entire contents of the axial cell ofanother young Nematogen (.25 mm 



long). Osmic acid. 

 Fig. 104. A germ-cell in process of producing the paranucleus [n'). The fig. has 

 not been correctly reproduced. The black dots separating n' from the 

 central nuclear portion should have been more elongated. They appear- 

 ed to represent remnants of spindle-fibres. Acetic acid. 

 Fig. 105. The paranucleus [n] completely eliminated. Acetic acid. 

 Fig. 100. The paranucleus lies detached by the side of two cells which have 

 arisen by division of the cell m in fig. 105. The membrane of the para- 

 nucleus is very thin. Acetic acid. 

 Fig. 107. A similar stage, in which the paranucleus has attained a distinctly 



double-contoured membrane. Acetic acid. 

 Fig. 108, 109. Two of the three young Infusorigens found in a Rhombogen 1 mm 

 long. The two cells [g) of figs. 106, 107 multiply by division, and give 

 rise to a group of cells consisting of a peripheral layer and a central 

 cell. The paranucleus increases in size, and its membrane becomes 

 very thick. Acetic acid. 

 Fig. 110. Entire contents of the axial cell of a young Rhombogen (1.15 mm long). 

 The central nucleus [ne], the paranucleus [n'], and the Infusorigen. 



