PLASMA-STRUCTURE IN EGG OF HYDRACTINIA 191 



II. REVIEW OF SCHAXEL'S WORK 



Since Schaxel's results are rather complicated, it may be well 

 to review them briefly here. His interesting conception has been 

 derived from observations on the eggs of animals from widely 

 varying groups (Hydrozoa, 'lib; Sc5^hozoa, '10; echinoderms, 

 '11a; annelids, '12; ascidians, '09) in all of which hedescribes essen- 

 tially the following conditions. After the last oogonial division 

 the nucleus is reconstructed in the typical fashion, that is, the 

 chromosomes elongate as smooth threads to form a bouquet- 

 stage. These threads then lose their smooth contour, become 

 granular, and, by further diffusion, soon form a typical granular 

 reticulum, the threads of which as a rule center in the nucleolus. 

 Only a. small layer of protoplasm (which at this time takes an 

 acid or 'plasma' stain) surrounds the nucleus. This is the 'pre- 

 emission stage' and the protoplasm is said to be in a state of 

 'primary achromasie.' 



This stage merges gradually into the next or 'emission' stage, 

 characterised by the accumulation of chromatin-granules on the 

 nuclear net, especially at those points where the threads of the 

 net touch the nuclear membrane. At the same time, by filtration 

 through the membrane, groups of granules collect on the outside 

 of the nucleus directly against the wall, at the ends of linin-threads 

 which are poor in granules. The stage of actual emission of 

 material is of rather brief duration and at its close the protoplasm 

 is in a state of 'chromasie.' This 'extra-nuclear chromatin' 

 stains with basic dyes. 



The 'post emission' stage follows rapidly and is characterised 

 by further reconstruction of the nucleus, spreading of the extra- 

 nuclear chromatin throughout the protoplasm ('complete chro- 

 masie') and rapid growth and difl"erentiation of the yolk. The 

 latter is formed indirectly from the extra-nuclear chromatin, as 

 a small island of yolk in a 'nest'- of granules, at the expense of 

 which it increases. In his earliest paper on ascidians, Schaxel 

 ('09) describes a 'secondary achromasie' of the protoplasm of 

 the mature egg, any extra granules not used in the formation 

 of the yolk being absorbed by the phagocytic action of the test- 



