Castle. — Ciona intestinalis. 



PLATE I. 



All Figures represent sections ; magnification, 560 diameters. Yolk granules are 

 not represented, except in Fig. 2. 



Fig. 1. First maturation spindle, and formation of first polar globule. 



Fig. 2. Portion of section through recently impregnated egg. The spermatozoon 



lies at the centre of a region free from yolk granules. 

 Fig. 3. Second maturation spindle. 



Fig. 4. Section through the same egg in region of male pronucleus. 

 Fig. 5. Impregnated egg ; male and female pronuclei visible in the same section. 

 Fig. 0. Conjugation of pronuclei, viewed in the direction of the axis of the first 



cleavage spindle, which is in process of formation. (Cf. Plate III. 



Fig. 13.) 



