410 E. R. Downing, 
the former a well-nourished budding Hydra, the latter an animal in 
the early stages of testicular development. Fig. 12 gives a still 
earlier stage in which the interstitial cell is dividing, no spermary 
having yet formed on the animal. Fig. 15 was from an animal 
having testes, although this particular section was through a region 
where the testis was just beginning to form. Fig. 13 however is 
a section at the base of a well developed testis. The endoderm 
cells, it will be noticed, are highly vacuolate. When Hydra is well 
fed, nutritive material is ingested and digested by the endoderm 
cells and passed on to the ectoderm cells, where it is stored in 
granules in the peripheral portion. These granules are a golden 
brown in color and are likely in the nature of fat as they stain very 
dark with osmic acid (Fig. 14). All observers have noted that brown 
Hydra when starved lose their color. This change is due, it seems 
probable, to the use of this stored food reserve during starvation. 
For such pale emaciated Hydra I find are always without the peri- 
pheral layer of granules that stain intensely with osmic acid. The 
Hydra that are bearing many testes are in the same condition. But 
in addition to absorbing this stored food material during the repro- 
ductive season there is also passed to the ectoderm nutritive material 
from the endoderm. 
Many of the endoderm nuclei contain spherical particles which 
do not stain with the osmic acid but do take a deep stain with 
iron haematoxylin or any other nuclear stain. There are also in 
the endoderm cells masses of protoplasm containing such spheres 
from particles very minute in size up to droplets 2 or 3 w in 
diameter. Moreover among the cells at the base of this spermary 
are to be found accumulations of exactly similar droplets. The 
correct interpretation of this is that the nuclei of the endoderm cells 
elaborate a substance akin to nucleinic acid, which is passed out 
into the cell protoplasm and thence on into the ectoderm. No case 
of actual transition through the mesogleea has been seen, so that it 
cannot be stated whether the droplets are passed through it intact 
or whether they are first dissolved and reappear after transfiltration. 
The negative evidence would indicate the latter process. During 
life these streams of nutritive material between the spermatogonia 
give to the testes a striated appearance, the droplets appearing as 
lines of orange yellow material, which is the color during life of 
the nuclei of the cells at the base of the spermary. In stained 
section it is to be noted too that the nuclei at the very base of the 
