246 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



Fig. 136. Ovary immediately after egg laying, seen from below. From lobster No. 52, table 20. Tbe 

 oviducts are rilled with unextruded eggs; a few of these ova are also seen in tbe ovaries. 

 Immature eggs from this ovary are shown in fig. 134. The yellow flecks are the remains 

 of unextruded eggs of a former egg generation ; that is, they have been in the ovary two 

 years at least. Drawn in natural size and color from life. July 28, 1891. 



Fig. 137. Ovary of lobster No. 87, table 20, bearing external eggs. The latter have been laid about 

 six weeks (date of laying about July 10). The ovarian eggs possess a dark-green core and 

 lighter periphery. At the period of ovulation they are colorless, as shown in figs. 134 

 and 136. August 21, 1891. Drawn in natural size from life. 



Fig. 138. Ovary of female which has recently hatched a brood. Taken July 30, 1891. For description 

 of lobster see No. 95, table 20. The pea-green color is characteristic of the ovary at this 

 time. The contained eggs, one of Avhich is shown in fig. 133, are approximately one year 

 old. The difference in relative size between the ova shown in figs. 133 and 134 thus 

 represents a year's growth, while the relative difference in size between the ova shown in 

 figs. 134 and 135 represents only six weeks of summer growth. 



We thus see that a generation of ovarian ova grow very rapidly during the first sum- 

 mer following tbe last ovulation. They then enter upon a period of quiescence, growing 

 but slowly, like the external embryos during the succeeding winter. The second summer 

 following ovulation is marked by a second period of rapid growth, followed in turn by a 

 second period of quiescence during the succeeding winter. At the beginning of the third 

 summer after ovulation this generation of eggs is ready for extrusion. That the spawn- 

 ing periods are thus two years apart is a valid inference drawn from the study of the 

 anatomy of the reproductive organs. Yellow spots mark as before the remains of degen- 

 erate eggs which failed of emission at the last reproductive period. The characteristic 

 condition of the ovary shown in this drawing proves that annual breeding is an 

 impossibility. Drawn in natural size and color from life. 



Plate 39. 

 Fig. 139. Part of transverse section of ovary of lobster, No. 52, table 20, with external eggs in early 



segmentation, the ova having been laid about thirty-six hours. The peculiar glandular 



organs are now seen in the peripheral parts of the lobes. O. G., ovarian gland; O. W., 



wall of ovary. 36 times natural size. 

 Fig. 140. Part of transverse section of ovary of lobster No. 94, table 20. Glands absent; ovaries 



approaching maturity. 36 times natural size. 

 Fig. 141. Part of transverse section of nearly ripe ovary, from lobster No. 75, table 20. August 19, 1890. 



Tbe nucleus or germinal vesicle is shown in one of the nearly ripe eggs. (For more 



detailed drawing of nucleus, see fig. 160.) Bl. S., blood sinus; Ct, nodule of connective 



tissue. O. G., ovarian gland 22 times natural size. 

 Fig. 142. Part of transverse section of ovary of lobster No. 52, table 20, showing follicle cells which 



have wandered into the egg and are undergoing degeneration. Dg, vesiculated masses of 



chromatin, the fragments of degenerated cells; Bl. S., blood sinus containing blood 



cells. 457 times natural size. 

 Fig. 143. Part of transverse section of ovary, the same as in fig. 141, showing the gland-like organs. 



Bl. S., blood sinus (dotted line should be continued across gland). 211 times natural size. 



Plate 40. 

 Fig. 144. Eight pleopod of adult female lobster, seen from posterior surface. Drawn from alcoholic 



preparation, with camera and dissecting microscope, the cuticle being removed from one 



side to show distribution of cement glands in swimmerets. 4 times natural size. 

 Fig. 145. Fold of glandular epithelium from transverse section of ovary of lobster No. 75, table 20. 



From same as fig. 141. ys, body resembling yolk spherule. 190 times natural size. 

 Fig. 146. Transverse section of lobe of ovary shown in fig. 131, plate 38. From No. 2, table 32. 67 



times natural size. 

 Fig. 147. Part of transverse section of ovarian lobe from a lobster with external eggs near the point 



of hatching. The condition of this ovary closely corresponds to that shown in fig. 138. 



June 30, 1890. Bl. S., blood sinus. 36 times natural size. 



