DEVELOPMENT OP FLUSTRELLA HISPIDA. 441 



vSpermatogenesis and Oogenesis. 



In F lustre 11 a hi spiel a the zooecium is hermaphrodite, 

 but the spermatozoa are chiefly developed earlier in the year 

 than the ova. In February and early in March, however, 

 ova and spermatozoa are found to occur simultaneously in the 

 zooecium; the spermatozoa are in such cases fully developed, 

 while the ova are immature. PI. 22, fig. 1, shows a section 

 through a very young colony taken early in March ; ova are 

 seen to be present in one zooecium, and in the anterior jjortion 

 of the same zooecium s^Dcrmatozoa also occur. 



Early in February the colonies assume a very puffed and 

 spotted appearance, large dark-brown patches becoming 

 visible. On cutting a section of such a colony these brown 

 patches are found to be due to the presence of an immense 

 number of spermatozoa, which can be removed in the same 

 way as the ova by slicing off the front wall of the colony. 

 As has already been described by Calvet (8), the spermatozoa 

 are developed from the mesenchyme lining the lateral walls 

 of the zooecium, and the mother cells lie in masses close to the 

 front wall in the region of the tentacle sheath (PI. 22, fig. 1, T.). 

 When ripe the spermatozoa have the typical flagellate form. 

 Frequently masses of spermatozoa are seen to be lying 

 with their heads imbedded in a central mass of protoplasm, 

 and with their tails vibrating at the periphery. No attempt 

 has been made at present to work out the details of spermato- 

 genesis. The spermatozoa decrease in number towards the 

 middle of March, and they are uot in evidence after the end 

 of that month. 



The ovary lies at a point to the rear of and at a lower level 

 than that at which the spermatozoa are developed. It is 

 situated on a funicle passing from the meseuchymatous lining 

 of the lateral zocecial wall to the intestine (PI. 22, fig. 1, Ov.). 

 At first the young ovary shows no indication of cell-walls, but 

 consists merely of a protoplasmic mass containing numerous 

 large nuclei (PI. 22, figs. 1 and 4, N.). Cell-walls subsequently 

 arise in this protoplasmic mass, four or five of the ovarian 



