GERM CELLS OF COELENTERATES 13 



alveolar structure; the nucleus contains a more marked reticu- 

 lum of chromatin, and the nucleolus is much vacuolated. Such 

 an egg as that shown in figure 1 1 would be found in the pedicel 

 or in the base of the hydranth which is producing gonophores. 

 Figure 12 is an egg which has just reached the young develop- 

 ing gonophore, i.e., it is in almost its final position where it 

 ripens and develops. The cytoplasm is noticeably alveolar, not 

 deeply staining because of so loose a texture, and with a ring of 

 chromatic granules close to the nucleus which is abundant enough 

 to indicate considerable movement of nuclear substance into the 

 cytoplasm. The nucleus does not differ from the earlier condi- 

 tion save for an increase in size and an increase in the amount of 

 chromatin which results in a more marked reticulum. 



The egg shown in figure 13 is located in the gonophore and is 

 well started upon its growth, though not yet more than one- 

 fifth of the final volume of a ripe egg. It differs from a mature 

 egg mainly in size, the structure being quite similar. Large 

 yolk spheres occupy most of the cytoplasm, the granular cyto- 

 plasm not being very abundant, while chromatin material is 

 still passing from the nucleus in somewhat less abundance than 

 formerly. The nuclear reticulum shows regions of concentra- 

 tion of chromatin at the nodes of the network, and a large vacuo- 

 lated nucleolus similar to that of ealier stages is present, but not 

 represented in figure 13. In later growth the changes from the 

 above description are not great, yolk is produced to an enormous 

 extent and the egg is loaded down with it. The nucleus prob- 

 ably does not change greatly, though it was not studied in the 

 later growth phases. After the egg reaches the young gono- 

 phore the latter elongates, carrying the egg away from the hy- 

 dranth and at the same time finger-like extensions of the stem 

 surround the egg and supply nourishment to it during its later 

 growth. The growth is completed, and maturation, fertiliza- 

 tion, and development all take place within the gonophore, an 

 embryo in the form of a planula finally escaping. 



