54 Papers from the Marine Biological Laboratory at Tortngas. 



same series of eggs. In one type the chromosomes arose from the nuclear 

 reticulum (here the nucleolus was a plasmosome), in the other from a 

 chromatin nucleolus. Asterias presents no condition which can be reconciled 

 with either of the types described and figured by Wilson. 



Max Hartmann (1902) concludes for Asterias glacialis that "during the 

 growth-period of the ovarian eggs there occur ' vegetative nuclear altera- 

 tions/ the distribution of chromatin substance in the nucleus, and accumula- 

 tion of the same in the nucleolus. At the end of this period all the 

 chromatin and plastin is combined in the nucleolus, and out of this there 

 arise at the time of the shedding of eggs into the water with the appearance 

 of an astral structure and dissolution of the germinal vesicle, the chromo- 

 somes of first maturation division." 



K. Guenther (1903) reports the following in the case of Psamechinns 

 micro-tuber culatns and Holothuria tubulosa: " Der Nucleolus stellt einen vom 

 Kerngeriist ausgeschiedenen Tropfen, in den das Chromatin hineindringt um 

 sich in ihn zu sondern und fur seine Theilung zu ordnen," p. 23. He holds 

 that the chromatin of the germinal vesicle is collected and stored in the 

 nucleolus during the growth-period of the oocyte, that it undergoes there 

 possibly some physical and chemical changes, and so wanders forth again 

 at the time of maturation to give rise to the chromosomes of the first divi- 

 sion. He remarks further that the " Chromatin faden (hat) bei semen Aus- 

 wanderung eine kleine Vacuole zuriickgelassen, und wenn nun bei diese der 

 Kernsaft eintritt, so ist am Raum nicht verloren." 



T. H. Bryce (1903) states that in Ecliinus esculent-its "the chromatin 

 substance is at first confined to the nucleolus, and later leaves it to form the 

 chromatin basis of the nuclear network as a whole and therefore also of the 

 future chromosomes," but adds that the nature of his material makes it 

 impossible for him to deny or affirm the direct origin of the chromosomes 

 from the nucleolus. 



My own observations on the eggs of Asterias forbesii establish beyond 

 a doubt, I believe, the fact that while the chromosomes often appear to 

 arise from within the nucleolus, as described by Hartmann (1902) and Guen- 

 ther (1903) in certain echinoderms, they never really penetrate beyond the 

 surface of the nucleolus, at least to the extent that their individuality is lost 

 and their substance merged into the common chromatin substance of the 

 nucleolus. Study of the different stages throughout the growth-period 

 shows that the chromosomes always retain their identity, though they are 

 greatly decreased in size, and they mass together into a clump which often 

 attaches itself closely to the nucleolus, from whence the chromosomes pass 

 into the spindle during early stages of maturation. This phenomenon of 

 chromosome disposition is very similar to what Conklin (1903) has described 

 in Crepidula and Lillie (1906) in Ch&toptcrus. According to the former, 

 " the chromosomes, which are at first widely scattered through the nucleus, 



