The Development of Phascolosoma. 83 



and spermatogonia are detached from the reproductive organs in Fh. 

 vulgare from September to December. Mitosis does not occur in the 

 ovaries during the summer months, but I have seen evidences of the 

 detachment of oogouia from the ovaries in July. Oogonia and oocj^tes 

 'in all stages of growth are found in the coelomic fluid throughout 

 the summer. 



3. Breeding Season and Egg-laying. 



The breeding season of Ph. gouldii at Newport R. I. extends 

 from the middle of June to the middle of August and probably later. 

 Eggs were laid in the laboratory at Wood's Hole, Mass. in 1900 as 

 late as September 3. I am unable to explain the fact that the 

 Wood's Hole specimens, though kept under apparently the same 

 conditions as those employed at Newport and at Eoscoff with uniform 

 success, seldom lay. Thus, during the seasons of 1896 and 1897, I 

 did not succeed in inducing a single individual to lay at Wood's 

 Hole, though specimens kept for me simultaneously at Mr. Agassiz' 

 laboratory at Newport were laying abundantly. In 1900, during a 

 short stay at Wood's Hole, three layings occurred (Aug. 22, 29, and 

 Sept. 3); in 1902, although observations were constantly made from 

 the middle of July to the last of August, only one lot of specimens 

 made a deposit of eggs, which occurred on the first w^eek in August. 



The breeding season oi Fh. vulgare at Roscoif extends from the 

 middle of June to the middle of September. 



Specimens, which are kept free from mud or sand in dishes 

 containing clean, gently-flowing sea water, may be expected to lay 

 during the second night after their capture, w^hen the alimentary 

 tube has already voided its contents. This is almost the invariable 

 rule for Fh. vulgare during the breeding season, but Fh. gouldii 

 appears to lay as commonly during the first night as the second. 

 I have never observed the egg-laying of these animals in their 

 natural surroundings, either in the aquarium or in the tide pools of 

 the mud-flats where they live. 



Ova that are ready for maturation, having the spindle of the 

 first polar body in the metaphase, are swept from the coelom into 

 the nephridia by the action of the cilia, which give rise to strong 

 currents within the nephridium, setting from the nephrostome back- 

 ward towards its posterior extremity. This is a most interesting 

 process in that both the immature oocytes, which are present in 

 great numbers in the coelomic fluid; and the coelomic corpuscles are 



6* 



