430 CASWELL GRAVE 



and thither between the fertihzation membrane and blastula. 

 These granules were ultimately swept into the blastopore to 

 form a plug, 



Franklin Islands Asterid. From a single 'brood' of eggs and 

 embryos, collected off the Franklin Islands, J. E. Henderson 

 ('05) has described certain intermediate stages of the life his- 

 tory of an unnamed asterid, the structure of which indicates 

 that the comparatively enormous quantity of yolk with which 

 the egg is stored, either remains outside the blastomeres dar- 

 ing early development, as in meroblastic cleavage, or is extruded 

 from the cells later, as is the case in Ophiura. The following 

 quotations from Henderson's paper show that a process of yolk 

 segregation has been developed by this species, evidently very 

 different from any hitherto found in an echinoderm. "The 

 chief difference between the Asterina embryo and that of the 

 Franklin Islands species is that the latter is much larger in size 

 and have all the interstices of the body gorged with yolk." 

 "The yolk forms by far the largest part of the whole star-fish, 

 at least nine-tenths of the whole bulk is yolk. Stained with 

 eosin this becomes easily differentiated from the other tissues. 

 It is composed chiefly of large globular or irregularly shaped 

 masses, which are closely apposed to one another, leaving 

 few chinks intervening. This yolk not only fills up the center 

 but penetrates everywhere; in fact, the whole of the tissues would 

 seem to have been built up around it as, indeed, they really 

 are. It is found among the ectoderm cells, between the ecto- 

 dermic wall and the peritoneal wall of the coelomic spaces, and 

 among the cells of the gut-wall, while with the gut it composes 

 the main mass of the interior." "The gut-cells are oblong in 

 shape with irregular ends towards the luraen, and seem to be 

 engulfing yolk, as particles of yolk can be seen not only among 

 them but also in their substance." "Amoebocytes and tissues 

 of the mesenchyme" are found among the yolk in the segmenta- 

 tion cavity. 



Yolk segregation in other phyla. If we turn to representatives 

 of other phyla of the Animal Kingdom for examples of localiza- 

 tion and segregation of yolk substance during or preceding 



