Relation between Nucleolus and Chromosomes. 63 



chromatin has no affinity reveal only the plastin portion of the nucleolus 

 and as a much vacnolated structure. 



All the data at my command as a result of the study of the egg of 

 Asterias forbesii support the view that the nucleolus is a storehouse of re- 

 serve nutritive material, combining also the function of " nuclein laboratory ' 

 (Pick) in the sense that chemical alterations may transpire in the material 

 while thus stored in the nucleolus. 



COMPARISON WITH HIPPONOE ESCULENTA. 



Material for a comparative study of the present problem in echinoderms 

 was collected during a four weeks' stay at the Marine Biological Laboratory 

 of the Carnegie Institution of Washington at Dry Tortugas, Florida. It 

 was my intention to extend the investigation over many different forms. 

 Among at least ten different genera sufficiently abundant and apparently 

 equally favorable for similar study, Hipponoc esculcnta alone had ripe eggs 

 at the time I left the island on June 13. From the appearance of thegonads 

 at that time it seemed probable that most of these forms would not ripen 

 their eggs for several months. 



Hipponoc esculenta was apparently at the height of its breeding season 

 during May and the early part of June. Due to the smaller size of the egg, 

 and particularly to the fact that the oocytes mature in the ovary, this form is 

 much less favorable for a study of the maturation phenomena than Asterias, 

 where the process takes place after spawning and can be readily observed 

 and controlled in the free egg. Unsuccessful attempts were made to induce 

 the immature oocyte of Hipponoe in sea-water to form the polar bodies by 

 agitation, the addition of sperm, and the addition of various salts and acids. 

 However, the addition of a drop of HC1 to a dish of sea-water containing 

 mature eggs caused a small percentage to develop through the early cleav- 

 age stages. Controls of eggs from the same batch and in the same water 

 without the HC1 showed no segmentation stages. 



As in Asterias, there is in the ovary of Hipponoe a striking lack of tran- 

 sition stages between the oogonia and the full-grown primary oocyte, giv- 

 ing evidence of the great brevity of the growth-process. The infrequency of 

 the oocytes in maturation shows that this process also is consummated very 

 quickly. Batches of eggs taken from the ovary of even the smallest speci- 

 men yielded at the highest only about 10 per cent of immature ova. In the 

 larger specimens all the ova were fully matured. A section through the 

 ovary of the latter revealed a layer of oogonial cells, a few immature full- 

 grown oocytes, and a large number of mature ova. The female pronucleus 

 is comparatively larger than that of Asterias, and it is characteristically 

 devoid of a nucleolus (fig. 95). Toto mounts of eggs show two small polar 

 bodies. Sections of the first polar body reveal an attempt at a second 

 division (fig. 94). 



