186 GERM-CELL CYCLE IN ANIMALS 
Neritina which finally reach the velar cells. It is 
also probable that Fol (1880) observed similar gran- 
ules in the 16-cell stage of Planorbis. In the same 
category, no doubt, belong the bodies figured by 
Fujita (1904) in the 4-cell to the 16-cell stages of 
Siphonaria lying at the vegetative pole, and the 
““Ectosomen” described and figured by Wierzejski 
(1906) in Physa. These granules appear at the vege- 
tal pole in the blastomeres of Physa during the 
second cleavage; are at first embedded in the ento- 
derm mother cells, but finally become localized in 
the ectoderm cells. They periodically appear and 
disappear, and may, as suggested by Wierzejski, 
represent only ‘‘eine besondere Erscheinung des 
Stoffwechsels” (p. 536). 
Similarly in the rotifer, Asplanchna, Jennings (1896) 
has traced a “cloud of granules” from the eight-cell 
stage until the seventh cleavage, when this mass 
forms part of the smaller entodermal cell. In Lepas 
there has also been recorded (Bigelow, 1902) a segre- 
gation of granules in one blastomere. Many other 
substances granular in form have been described in 
the eggs of animals, some of them at least having 
migrated there from the somatic tissue. Blockmann 
(1887) discovered a number of bacteria-like rods 
in the undeveloped eggs of Blatta germanica; these 
rods multiplied by division and were considered sym- 
biotic bacteria. ‘“‘Bacterienartige St&bchen” were 
also noted by Heymons (1895) in the eggs of Pert- 
planata orientalis and Ectobia livida; these sink into 
the yolk and disappear. More recently a report of 
