12 Papers from the Marine Biological Laboratory at Tortugas. 
SUMMARY AND CONCLUSION. 
In Echinaster crassispina the chromosomes are derived exclusively from 
the nucleolus. In Ophiocoma pumila the chromosomes arise exclusively 
from the nuclear reticulum. The germinal vesicle of both species con- 
tains a chromatic nucleolus. There are here two extreme types. Asterias 
forbesii furnishes an intermediate type in that here the chromosomes assume 
a more or less intimate connection with the nucleolus prior to maturation 
and receive substance therefrom. Eggs of Toxopneustes variegatus, parthe- 
nogenetically developed after treatment with MgCl,, according to Wilson 
yield the two extremes in different sets, there being in one case present a 
plasmosome and in the other a chromatic nucleolus. It appears that differ- 
ent forms of echinoderms differ in the matter of the origin of the prematura- 
tion chromosomes. In some species the chromosomes arise from a chroma- 
tin-nucleolus, in others from a chromatic reticulum, and in still others in part 
from one source and in part from the other. Again, the eggs of different 
forms appear to differ in that some have only a chromatin-nucleolus, without 
distinct plastin ground-substance, resting in an achromatic nuclear reticulum 
(Echinaster) ; others possess both chromatin-nucleolus and plasmosome as 
well as a chromatic nuclear reticulum (Ophiocoma) ; and still others possess 
a double nucleolus (chromatin nucleolus and plastin ground-substance), with 
the chromosome complex gathered in a mass in the achromatic reticulum 
(Asterias). 
The chromosomes thus arise inconstantly in different species from any 
part of the germinal vesicle that contains the chromatin material, and this 
may be either nucleolus, nuclear reticulum, or both. The function of the 
germinal spot then appears, in part at least, to be that of a storehouse of 
material which is to contribute to the formation of the chromosomes. What 
chromatin is not so employed is resorbed by the cytoplasm, probably return- 
ing to the elements from which it was elaborated and serving as a food mate- 
rial. There appears nothing here to support or confirm the theory of the 
individuality of the chromosomes, but rather much to arouse suspicion 
regarding the theory. But one may take refuge in the idea of “centers of 
chromosome activity’ as suggested by Davis,t and so the chromatin may 
perhaps be regarded as merely the garb for the determinants of inheritance, 
and the characters that arise in their manifold variations as the result of a 
quantitative as well as a qualitative distribution of chromatin. 
* Davis, B. M., 1905. Studies on the plant cell. Am. Nat., Voli 30. 
