No. 2.] THE SEA-URCHIN EGG. 469 



VI. General. 



The Q.%^ of Toxopneiistes shows with striking clearness the 

 fact, which has been urged by several observers in other cases, 

 that all the parts of the cell show a most intimate morpho- 

 logical connection and may be regarded as specially differen- 

 tiated areas in a common structural basis. This basis is here 

 a thread-work, the fibres of which are composed of definite 

 granules or microsomes, suspended in a clearer substance of 

 different staining power. While the precise nature of this 

 structural basis in general is still in dispute, it is now pretty 

 generally admitted to form either a network or an alveolar 

 structure that extends throughout the cell, forming outside the 

 nucleus the so-called cyto-reticulum and within it the linin net- 

 work. According to my observations in Toxopneiistes, which 

 agree closely with those of Reinke, Eismond, Heidenhain, and 

 many others, the entire system of astral rays and spindle-fibres 

 arises solely through a morphological rearrangement of the 

 elements of this reticulum, as may be observed, step by step, 

 in the formation and later history of the sperm-aster. More- 

 over, the centrosome itself is but a differentiated portion of the 

 same reticulum, as appears with special clearness in the large 

 centrosphere of the sea-urchin ^gg, and has been urged on 

 various grounds by Biitschli, Watase, Reinke, and Eismond. 



I can find no sufficient grounds for regarding the nucleus in 

 a different light, and the evidence of its close morphological 

 relationship with other portions of the cell is steadily accumu- 

 lating. It is true that the chemical composition of the nucleus 

 is highly characteristic (though nuclein is known to exist in 

 cytoplasm as well) and that its morphological independence is 

 very marked, but in neither of these regards is it a unique and 

 isolated structure. Heidenhain has produced evidence that 

 the chromatic network contains substances transitional in a 

 chemical sense between chromatin ("basichromatin " of Heid- 

 enhain) and linin (" oxychromatin ") ; and the nature of the 

 transition is placed in a very clear light by the researches of 

 Kossel, Malfatti and Lilienfeld on the relation between nuclein 

 and nucleo-albumins, the former containing a high percentage 



