13 



forward of the terminal portions. Where the dorsal and ventral fibres 

 meet in the rachal and mediad lines, they sometimes anastomose, and 

 at other times cross one another to end in a point. 



4) A cellular stratum, differing from the 2nd stratum only 

 in the more or less complete absence of vaso-fibrous tissue, and in 

 having no longitudinal muscle-fibres. Both the 2nd and 4th stratum 

 are thickened somevv^hat along the rachal side, thus forming a sort of 

 rachis. 



The lining epithelium, consisting of fusiform cells often 

 widely separated from one another by intercellular intervals , corre- 

 sponds nearly to what Ley dig found in Piscicola. These cells mul- 

 tiply and form a massive ridge of cells along the inner surface of the 

 rachal thickening. This massive portion of the lining epithelium may 

 be called the germogen (Balfour) 2. 



The Egg-strings are derived from the germogen, which is com- 

 posed of a main median ridge and several small and younger ridges on 

 each side. The median ridge or string is quite irregularly marked off 

 into parts, each of which, as it grows larger, assumes the form of the 

 egg-string, and finally becomes detached. The median ridge is re- 

 placed by the coalescence of the younger ridges of the germogen. 



The germogen is composed of membraneless cells, the outlines of 

 which are sometimes obscure, but for the most part tolerably well 

 marked. 



Some of these germ-cells are destined to give rise to the ova, while 

 others appear to undergo degeneration and to serve as nourishment for 

 the latter. 



The primordial ova are formed somewhat as in Piscicola as 

 given by Ludwig. One of the germ-cells begins to enlarge while its 

 nucleus, by repeated division, gives rise to a cluster of nuclei. A sort 

 of follicle is thus formed, the contents of which consists of the cell- 

 protoplasm and a nest of nuclei. Around one of these nuclei, a cell-like 

 body of protoplasm, much clearer than the remaining protoplasm, becomes 

 clearly defined. This is the primordial ovum. The ovum soon be- 

 comes invested with a distinct membrane, and, growing at the expense 

 of the follicular contents, gradually comes to fill most of the follicular 

 space. The free nuclei and the protoplasm are probably all absorbed 

 by the egg-cell. 



Thus the egg and its follicle arise from a single germ-cell. 



One or more y o 1 k - n u c 1 e i are often found in the eggj analogous 

 to what has been found in the Amphibian egg. 



2 I use the word in a less restricted sense than Balfour. 



