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THE AMEBIC AN NATURALIST [Vol. XL VII 



simple, all of whose colonies (and included statoblasts) 

 carry the same germplasm and compound, those whose 

 colonies and statoblasts carry more than one kind of 

 germplasm. These can not, in general, be distinguished 

 by gross appearance. 



Eecent studies have shown that parts of organisms 

 that are derived from the same germplasm (without the 

 intervention of sexual reproduction) are much more con- 

 stant in their morphological features than parts of or- 

 ganisms that, however closely related, are each the prod- 

 uct of the union of two germ cells. For germ cells are 

 necessarily more or less unlike, and may be very unlike, 

 and, consequently, their progeny will be variable. We 

 should expect then (to return to the Pectinatella masses) 

 to find them of two kinds, (a) with a relative constancy 

 in the modes of the distributions of the statoblast-hooks, 

 and (b) with two or more modes (centers of variation) 

 of statoblast-hooks in different colonies from the same 

 mass. 



Historical 



The first statistical study of variation in the number 

 of hooks per statoblast made was, in 1900, by one of us. 

 In 1906, Miss Alice W. Wilcox showed that a Pectinatella 

 mass is derived from statoblast-embryos the products 

 of which repeatedly divide, move from each other and, 

 as they enlarge, come in contact again. Her study makes 

 it probable that a mass may be derived either from one 

 or from two or more independent statoblast-colonies. 

 Braem (1911, pp. 321, 323) refers to a mass derived from 

 about 80 statoblasts, but the product of a great propor- 

 tion of them perished. He has also a mass derived from 

 only one statoblast. Braem points out that the number 

 of hooks per statoblast tends to increase with the age of 

 the colony and of the whole mass. He considers a pos- 

 sible difference in heredity tendencies inside the differ- 

 ent colonies and concludes that this factor is small as 

 compared with other factors, above all, temperature of 

 the water. 



