CRANQON VULGARIS. 149 



testimony of his sections to support his view. He fur- 

 ther thinks (p. 228) that the germinal area is formed by 

 a similar contraction and consequent thickening of the 

 cells, but I am confident that in Crangon the germinal 

 area is due largely if not wholly to the mode of forma- 

 tion described above. Whether there be a contraction as 

 well I cannot say. 



At stage C there appears another structure, the mean- 

 ing of which I do not understand. On the dorsal surface 

 of the egg, about opposite the mouth in the median line, 

 one sees a patch of about twenty or thirty cells much 

 smaller than those of the surrounding blastoderm. This 

 I have termed a "dorsal organ" for the reason that it 

 agrees with all other structures known by the same name 

 in being unintelligible. In sections (fig. 19) it is seen 

 to be made up of columnar cells with elongate nuclei, the 

 cells being arranged in a radial manner as though an in- 

 vagination were taking place. The development, so far 

 as my sections show, goes no farther and in the later 

 stages the cells of this region are not distinguishable from 

 those of the surrounding ectoderm. This structure, as 

 shown in fig. 19, at once recalls the early stages of 

 the dorsal organ as described by Bullar ('78) in Cymo- 

 thoa. It bears less resemblance to the dorsal organs of 

 other forms. 



The next stage (F) is shown in figs. 17 and 18, which 

 need no extended description. The most prominent fea- 

 tures are the beginning of the deposition of pigment, the 

 appearance of the edge of the carapax and the beating of the 

 heart. The deposition of pigment brings plainly into view 

 the compound eyes as well as the median ocellus (oc). 

 There also appears in either half of the cephalic ganglion 

 a double pigment spot (pg, fig. 17) which so simulates an 

 ocellus that I have been unable to decide whether it were 



