290 



SCIENCE. 



[N. S. Vol. XXI. No. 530. 



Fig. 3. — Relations of the ehiomosomes; formation and distribution of protoplasmic stuffs in 

 later stages. A, union of the gorm nuclei (each assumed to have four chromosomes). B, C, 

 division of the chromosomes, with equal distribution of the paternal (^J) and maternal (5) 

 products. D, scheme of nucleus at any later stage, with four paternal and four maternal 

 chromosomes (corresponding or homologous chromosomes connected by dotted lines). E, 

 actual outline (after Mead) of egg of Amphitrite consisting of upwards of 64 cells (nuclei 

 schematized). Entoblast-cells unshaded, primary mesoblast cross-hatched, trochoblasts 

 (ciliated cells) dotted, cells of ventral plate (ventral nervous system, etc.) black; the other 

 cells belong to the ectoblast. 



as yet only an assumption, not a completely 

 demonstrated fact. 



These entities are bodies known as 

 'chromosomes,' and are represented in the 

 diagrams by the rods in the nuclei.* I 



* In point of fact the chromosomes are, as a 

 rule, only distinctly visible at the period of cell- 



can not within the limits of this address 

 attempt to do more than touch on a few 

 of the discoveries of recent years regarding 

 the chromosomes, though I think they may 



division. In the diagram they are represented 

 quite schematically, as if visible in the resting 

 nuclei. 



