No. 2.] THE OVARIAN EGG OF LIMULUS. 149 



the fully grown yolk spheres can be observed, not in the same 

 egg, but in a series of eggs, according to the time which has 

 elapsed since their discharge. 



In this stage the nucleolus has disappeared, and the greatly 

 increased yolk spheres often render it difficult to find any trace 

 of the germinal vesicle, except in the first part of the period, 

 when it still can be seen immediately under the egg membrane 

 or comparatively close to it. 



Degenerative processes. — In the third stage it sometimes 

 happens that the egg, instead of being discharged into the 

 ovarian tube, undergoes degeneration. This has been observed 

 occasionally in material collected both at Woods Holl and at 

 New Haven ; but it was most pronounced in the ovaries of 

 those animals which were obtained from the aquaria of the 

 United States Fish Commission at the World's Columbian 

 Exposition in Chicago. 



These animals had been kept in confinement for at least six 

 or seven months. It is probable that they had suffered from 

 lack of nourishment, as well as from other disturbing influ- 

 ences incident to a long confinement. 



The ovarian tubes of these animals were filled with mature 

 eggs, and oviposition had probably been prevented by their 

 captivity. Many of the larger follicular eggs show the regres- 

 sive metamorphosis referred to. 



The metamorphic process appears to take place in two ways : 

 first, by the gradual absorption of the egg without the inva- 

 sion of cells ; second, by the appearance, within the egg, of 

 innumerable nuclei (PL XIV, Fig. 30). 



In the latter case the germinal vesicle, so far as observed, 

 is in all cases absent. On their first appearance the nuclei 

 are found at the proximal pole, where, in this stage of the 

 egg, the germinal vesicle is normally found. With the increase 

 of these nuclei they spread throughout the central part of 

 the egg ; and, without at first producing any abnormal appear- 

 ances of the yolk, gradually fill the entire egg (PI. XIV, Fig. 

 30). Simultaneously with this, one or several layers of well- 

 defined, polygonal cells surround the egg, between the outer 

 tunic and the egg membrane, in many cases giving the appear- 



