. The germ-cell cycle in animals . Cells. 146 GERM-CELL CYCLE IN ANIMALS of divisions a number of nuclei which migrate to the periphery, as is the rule in insect development. The " nucleolo " remains during this cleavage period unchanged near the posterior end (Fig. 44, B) ; then, when cell walls appear, it becomes distributed among several of the cells thus formed. These multiply less rapidly than the other em- bryonic cells and are the only cells that give rise to the germ cells in the adult. It is thus obvious that there is here an early segregation of germ cells and that these ge
. The germ-cell cycle in animals . Cells. 146 GERM-CELL CYCLE IN ANIMALS of divisions a number of nuclei which migrate to the periphery, as is the rule in insect development. The " nucleolo " remains during this cleavage period unchanged near the posterior end (Fig. 44, B) ; then, when cell walls appear, it becomes distributed among several of the cells thus formed. These multiply less rapidly than the other em- bryonic cells and are the only cells that give rise to the germ cells in the adult. It is thus obvious that there is here an early segregation of germ cells and that these germ cells dif- °ora. A. Egg with'germ- f cr from the somatic inal vesicle (A) and "Nucleolo" (A^). ccUs in the pOSSCS- B. Egg containing many cleavage nuclei. „ . p .1 C. Formation of primordial germ cells SlOn OI part OI tne f^i ^) ^"tnl"^ """"^ °^ '"' ''^®- '^™"' disintegrated " nu- Sihestri, 1908.) ° ; The polyembryonic species described by Silvestri are Copidosoma (Litomastix) truncatellus and Agenias- pis (Encyrtus) fuscicollis. The eggs of these species when laid are vase-shaped (Fig. 45), the posterior end corresponding to the base of the vase. Here also a germinal vesicle and "nucleolo" are present, the latter almost always near the posterior end. Parthenogenetic eggs were found to produce Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Hegner, Robert William, 1880-1942. New York : The Macmillan Company
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectcells, bookyear1914
