II 



MUSCINE^— HEPATIC JE—MAKCI J AXTI ALES 



55 



pressed (Fig. 19, C), so that this may acojunt for Janczewski's 

 error in stating that the number was always four, as the nuclei 

 in unstained sections might very easily he (Aciiocjked. The 

 cover cells are somewhat smaller than in Riccia and do not 

 usually undergo as many divisions, there being seldom nvjre 

 than six in all. In Targionia (hig. 23, A), and Strasburger 

 ((21), p. 418) observed the same in MarcJiaiitia, the ripe n^^ 

 shows a distinct ''receptive spot," that is, the upper ])art of the 

 unfertilised egg is comparatively free from granular cyto])lasm, 

 while the lower part, about two-thirds in Targionia, is much 

 more densely granular. The nucleus is not very large and has 

 very little chromatin. The nucleolus is large and distinct and 



/ A, 



D 



Fig. 19. — Targionia hypophylla. A, Longitudinal section of the apex of the thallus, 

 with young archegonia (ar), X525; x, the apical cell; B, young, C, older archc- 

 gonium in longitudinal section; D, cross-section of the archegonium neck, X5-5- 



Stains very intensely. As the archegonium of Targioiiia 

 matures, its neck elongates rapidly and bends forward and 

 upward, no doubt an adaptation to facilitate the entrance of 

 the spermatozoid. A similar curving of the archegonium neck 

 is observed in other forms wdiere the archegonium is upon the 

 lower side of the receptacle. 



After an archegonium (or sometimes several of nearly 

 equal age) is fertilised, the growth in length of the thallus stops. 



