512 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENGES. 



Plate XXV. 



Fig. 1. Surface view of segmenting egg of Hippa talpoiden. Thirty-two yolk pyramids present. 

 X38. 



Fig. 2. Embryo of Hippa talpoides, showing optic disks and thoracic-abdominal plate. x38. 



Fig. 3. The central part of a transverse section of the ovary of the lobster, Homarus americanus, 

 to show the progressive development of ova ; from the same series as that repre- 

 sented, with less enlargement, in Fig. 6. Ovary taken in January. x281. 



Fig. 4. Section of egg of Hippa talpoides in yolk segmentation. Sixty-four yolk pyramids pres- 

 ent. X 70. 



Fig. 5. Part of segmenting egg of Alpheus minor, showing a single large nucleus and two smaller 

 nuclei. Compare with Fig. 23. x281. 



Fig. 6. Central portion of transverse section of ovary of the lobster, coiresponding nearly to that 

 shown in Fig. H, showing the germogenal areas and the irregularly radiating blood 

 sinuses. The diameter of the entire ovary is about twice that of the part represented. 

 The largest peripheral ova have an average diameter of about one thirty-third of an 

 inch, and their contents is only about one-eighth that of the ripe egg. x 70. 



Fig. 7. Egg-nauplius embryo of Hippa talpoides. Appendages appear as simple buds. x38. 



Fig. 8. Post-nauplius stage of Hippa. Abdomen bilobed at tip. Buds of at least three pairs of 

 postmaudibular appendages. Figs. 1, 2, 7, and 8 are made from pen-and-ink sketches, 

 and show only the general appearance of the embryo and its relation to the yolk. 



REFERENCE LETTERS. 



Ah. I'., thoracic abdomiual plate. 



B. C, blood cell. 



lil. S., blood sinus. 



Ch., chitinons eggshell. 



Ch. jr., limiting membrane of blood sinus. 



Ct. S., ovarian stroma. 



E. /., egg follicle. 



F. C, egg follicle. 

 Ger., germogenal area. 



/. E., ovarian stroma (undifferentiated). 



0, o^—Qi', nuclei of ovarian stroma and developing eggs. 



0. D., optic disk. 



0. L., optic lobe. 



T. P., yolk pyramid. 



T. S., yolk spherule. 



Vac., yolk vacuole. 



