STUDIES ON GERM CELLS 479 



many insect eggs before fertilization is accomplished, and even 

 before the oocyte has reached its maximum size. We know that 

 in Chironomus the 'Keimwulst' (Ritter, '90) or 'Keimbahnplasma' 

 (Hasper, '11) is present when the egg is laid, at which time the 

 pronuclei as a rule have not yet fused. This is true also of the 

 'Dotterplatte' in Calliphora (Noack, '01). There can be little 

 doubt, however, that these substances are present as such in the 

 eggs before fertilization, judging from our knowledge of the his- 

 tory of similar materials in the eggs of other insects. The 'pole- 

 disc' in the eggs of Chrysomelid beetles (Hegner, '08; Wieman, 

 '10a) and the 'polares Plasma' in Miastor (Kahle, '08; Hegner, 

 '12) are recognizable some time before fertilization and cannot 

 therefore arise because of any influence exerted by the sper- 

 matozoon. Moreover, in Miastor the eggs thus far examined 

 have all been parthenogenetic. In parasitic Hymenoptera the 

 'nucleolo' leaves the germinal vesicle in both fertilized and 

 parthenogenetic eggs before the egg is laid. In only one animal, 

 not an insect, has a similar occurrence been noted, namely, in 

 Polyphemus, where, according to Kiihn ('11, '13) the Keim- 

 bahn-determinants consist of the remains of one or more nurse 

 cells (fig. 18). In the Daphnidae (Weismann and Ischikawa, 

 '89) the 'Paracopulationszelle' arises from material cast out by 

 the germinal vesicle; in Aequorea (Haecker, '92) the 'Metanucleo- 

 lus' is likewise derived from the germinal vesicle; in Ascaris 

 (Boveri, '92) chromatin diminution occurs during the two to 

 four-cell stage; in Cyclops (Haecker, '97, '03) and other copepods 

 (Amma, '11) the 'Aussenkornchen' or 'Ectosomen' become 

 visible soon after fertilization (Diaptomus), but usually not until 

 the pronuclei fuse (other species); in Sagitta the 'besonderer 

 Korper' (Elpatiewsky, '09, '10) or 'Keimbahnchromidien' (Buch- 

 ner, '10b) appear to arise de novo after fertilization, although, 

 if Buchner's contention that they are the remains of the accessory 

 fertilization cells be correct, they should be classed with the 

 'Nahrzellenkern' described by Kiihn ('11, '13) in Polyphemus. 

 It is thus evident that the Keimbahn-determinants become 

 visible, wherever they have been described, either just before 



