CRANGON VULGARIS. 105 



the unsegmented ovum. The character of the protoplasm 

 and the yolk need but a word. The vacuoles in the for- 

 mer I attribute to the action of the reagents. In the lat- 

 ter the yolk globules have become largely confluent and 

 have lost the spherical shapes which are seen in the fresh 

 egg. The round marks are oil globules. The whole yolk 

 stains faintly but I have not thought it necessary to repre- 

 sent it. 



After the second protoplasmic segmentation is effected, 

 the first segmentation furrows appear, the one following 

 close upon the other. The first to appear corresponds in 

 its direction to the first nuclear division, the second is at 

 right angles to it. Though well marked when viewed from 

 the surface, these furrows are in reality shallow grooves 

 which affect but the superficial layers of the deutoplasm 

 and which never have the depth of those occurring in many 

 if not in most decapods (e. g., Palsemon, Astacus, Eupa- 

 gurus, Homarus, Cancer, etc.). In sections they show 

 but as superficial constrictions ; the mass of yolk never 

 segments. That this is not the result of the hardening re- 

 agent (Perenyi's fluid) is shown by the fact that yolk seg- 

 ments do not appear in eggs hardened with alcohol alone. 

 Still it does not follow that the segmented egg with un- 

 segmented yolk is a syncitium. The nuclei and the sur- 

 rounding protoplasm are completely separated and these 

 are the essential portions of the cells ; the yolk is second- 

 ary and adventitious and is to be regarded as occupying 

 an extracellular position not only in Crangon but in many 

 other cases, Balfour's remarks ('80, p. 98) to the con- 

 trary notwithstanding. 



The general features of a decapod segmentation have 

 been detailed so often (Haeckel, '75; Ishikawa, 85 

 Mayer, '77; Faxon 79; etc.) that it is not necessary here 

 to follow it throughout in Craugon, which presents no 



