ETIPAGTTRUS. 549 



eighth stage cleavage is total but somewhat abnormal, the 

 nuclei dividing more rapidly than the blastomeres are 

 formed, so that it is not before eight nuclei are present 

 that segmentation occurs. The yolk is present in the 

 cells as small fat bodies. The separation of yolk matter 

 and protoplasm takes place on the egg dividing for the 

 fourth time, and the nuclei becomes peripherally 

 arranged, surface furrows indicating the boundaries of 

 the cells. From this point segmentation is superficial. 

 Gradually the centre of the egg breaks up and the proto- 

 plasm becomes confined to the single layer of cells on the 

 outside, which encloses the yolk. It is unnecessary to 

 follow the development further in detail, as it is quite 

 normal from this stage.* A germinal disc appears, in 

 the centre of which an invagination of the blastoderm 

 forms a shallow gastrula. In front of the gastrula is the 

 " anlage " of the abdominal region and further forwards 

 the paired " anlagen " of the cephalon. The mesoderm 

 proliferates from the cells in the front half of the 

 gastrula and spreads forwards into the cephalic region. 

 The gastrula cavity now closes and the hypoblast absorbs 

 the yolk matter, pressing the epiblast to a thin surface 

 layer. An invagination in front of the blastopore 

 becomes the mouth and fore-gut, while the blastopore 

 itself become the anus and hind-gut. The future mid- 

 gut is formed as usual from the invaginated hypoblast. 

 Post-embryonic development. — The breeding season 

 of Eupagurus is very extended, and at almost any time 

 of the year females may be seen with eggs attached. 

 The Zoeas are- to be found in tow-nets from April to the 

 end of September, and the Glaucothoe stage even later. 



* Further details may be obtained from P. Mayer's paper in 

 Jen. Zeitschr. f. Naturw., Bd. XL. p. 188, 1877, from which the above 

 account has been summarised. 



