PHYSIOLOGICAL RELATIONS OF NUCLEUS AND CYTOPLASM 255 



of such cells at one pole of the egg from which the latter is believed 

 to draw its nutriment (Fig. 58). A very interesting case is that of 

 the annelid Ophryotrocha, referred to at p. 114. Here, as described 

 by Korschelt, the egg floats in the perivisceral fluid, accompanied 

 by a nurst-cell having a very large chromatic nucleus, while that of 

 the egg is smaller and 

 poorer in chromatin. 

 As the egg completes 

 its growth, the nurse- 

 cell dwindles away and 

 finally perishes (Fig. 57). 

 In all these cases it 

 is scarcely possible to 

 doubt that the egg is 

 in a measure relieved 

 of the task of elaborat- 

 ing cytoplasmic products 

 by the nurse-cell, and 

 that the great develop- 

 ment of the nucleus in 

 the latter is correlated 

 with this function. 



Regarding the posi- 

 tion and movements of 

 the nucleus, Korschelt 

 reviews many facts 

 pointing towards the 

 same conclusion. Per- 

 haps the most sugges- 



tive of these relate to 

 the nucleus of the eg 



Fig. 115. Upper portion of the ovary in the earwig 



its Ovarian his- Forficula, showing eggs and nurse-cells. [KORSCHELT.] 

 tnrAr Tn manv nf the Below, a portion of the nearly ripe egg (), showing deuto- 



" plasm-spheres and germinal vesicle (gv). Above it lies the 



insects, as in both the nurse-cell (n) with its enormous branching nucleus. Two 



Cases referred to above successivel yy un g er sta S es of egg and nurse are shown above. 



the egg-nucleus at first occupies a central position, but as the 

 egg begins to grow, it moves to the periphery on the side turned 

 towards the nutritive cells. The same is true in the ovarian 

 eggs of some other animals, good examples of which are afforded 'by 

 various coelenterates, e.g. in medusae (Claus, Hertwig) and actinians 

 (Korschelt, Hertwig), where the germinal vesicle is always near the 

 point of attachment of the egg. Most suggestive of all is the case 

 of the water-beetle Dytiscns, in which Korschelt was able to observe 

 the movements and changes of form in the living object. The eggs 



