STUDIES ON GERM CELLS 435 



Die erstere Thatsache lasst freilich vermuthen, dass es immer die- 

 selbe Furchungszelle sei, mit welcher die Copulationszelle sich verbin- 

 det, die letztere deutet darauf bin, dass der Vorgang mit der geschlecht- 

 lichen Fortpflanzung etwas zu thun hat (pp. 182-183). 



The Keimbahn of Cyclops and some closely allied forms has been 

 very carefully investigated by Haecker ('97) and Amma ('11), 

 with results which are of particular interest so far as germ cell 

 determinants are concerned. In Cyclops, according to Haecker, 

 'Aussenkornchen' arise at one pole of the first cleavage spindle 

 (fig. 16, A, ak); these are derived from disintegrated nucleolar 

 material and are attracted to one pole of the spindle by a dis- 

 similar influence of *the centrosomes. During the first four 

 cleavage divisions the granules are segregated always in one cell 

 (fig. 16, B, kz); at the end of the fourth division these 'Aussen- 

 kornchen' disappear, but the cell which contained them can be 

 traced by its delayed mitotic phase, and is shown to be the 

 primordial germ cell. 



The most recent and complete account of the Keimbahn in 

 Copepoda is that of Amma ('11). This author studied the early 

 cleavage stages of eleven species of Cyclops, three species of 

 Diaptomus, one species of Canthocamptus, and one species of 

 Heterocope. Cyclops fuscus var. distinctus is made the basis 

 for the most detailed study, but short descriptions and figures 

 are presented of the others. In all of the sixteen species examined, 

 the stem-cell, which gives rise to the primordial germ-cell, may 

 be recognized, as Haecker ('97) discovered in Cyclops, first by 

 the presence of granules which do not occur in the other cleavage 

 cells, and later by a delayed mitotic division. The process is 

 essentially as described by Haecker. 



The following summary of the Keimbahn in Cyclops fuscus 

 var. distinctus is given by Amma: 



1. Wahrend der ersten Furchungsteilungen ist eine bestimmte 

 Folge von Zellen, die Keimbahn, durch das Auftreten von Kornchen, 

 die sich bei der Teilung jewels um einen Spindelpol der Teilungsfigur 

 ansammeln, gekennzeichnet (fig. 17, A). 



2. Die Kornchen oder Ectosomen entstehen immer erstmals wah- 

 rend des Stad.ums der Diakinese, vermehren sich wahrend der nachst 

 folgenden Phasen noch bedeutend und versclimelzen gegen das Ende 



