FURTHER EXPERIMENTS ON THE METHODS OF EGG- 

 LAYING IN AMPHITRITE. 



JOHN W. SCOTT. 



INTRODUCTION. 



On excursions, taken in connection with the course offered 

 to students studying invertebrate zoology at Woods Hole, I 

 have been impressed with the large number of forms not used 

 for investigation. I believe this must be because little is known 

 of their life-history and habits, because many of them are fairly 

 abundant. With this idea in view, I recorded in a recent paper 

 ('09) the results of some observations made upon the egg-laying 

 habits of one of the marine annelids. In the form studied, 

 Amphitrite, the germ cells arise in the typical way, i. e., from the 

 coelomic epithelium. Very early these dehisce into the body 

 cavity and mix with the coslomic corpuscles. In some annelids 

 as Nereis, the eggs escape by a rupture of the body wall. In 

 Amphitrite, however, they pass to the exterior through certain 

 nephridia that are highly modified to form gonaducts. In the 

 paper mentioned above it was shown that Amphitrite deposit 

 eggs at recurring periods that bear a close relation to the time 

 of spring tides. It was further shown that at the time of ovi- 

 position, the body cavity contains floating free, not only the 

 mature eggs and corpuscles but also the younger eggs in various 

 stages of development. A single period of egg-laying occupies 

 from 30-60 minutes, and most all eggs when extruded are in 

 the metaphase of the first polar spindle. A few large, though 

 unripe, eggs always escape especially toward the latter part 

 of the period. In Fig. I is shown the comparative size and shape 

 of various bodies found in the coelome at this time. It will be 

 noticed that the eggs when first set free in the coelome are smaller 

 than the red blood cells, yet neither cells nor eggs of this size 

 ever escape during oviposition. Indeed, comparatively few of 

 the large unripe eggs pass out through the nephridia. The 



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