260 BUMPUS. 



EXPLANATION OF PLATE XVIII. 



Fig. I. Ventral view of hinder part of thorax of a female lobster. The Roman 

 numerals indicate the third, fourth, and fifth ambulatory appendages. Natural size. 



Fig. 2. Receptive apparatus as seen from the right side, the right half having 

 been removed. Natural size. 



Fig. 3. Surface view of egg in stage represented on PI. XIV., Fig. L. X 60. 



Figs. 4-7. Transverse sections made through embryo, as indicated by the hori- 

 zontal lines in Fig. 3 (4-7)- X 200. The ectoderm is colored deep gray. In Fig. 7 

 the entoderm is seen working its way into the yolk. 



Fig. 8. Longitudinal section through median line of same stage as Figs. 3-7. 

 X 200. The entoderm extends deep into the yolk as a nucleated reticulum. The 

 cells arranged in an irregular oval, around the end of the line Pb, enclose a peculiar 

 plasma-like tract, which was unfortunately omitted by the lithographer. 



