15 



In the ooecia of Mel. lamellosa (pi. VII, figs. 20—22) however, only a few zooecial 

 areas are seen in the proximal part while in the rest of the cavity the zooecia 

 are only represented by a number of more or less open tubes. In opposition to 

 the ooecium of Mel. magnifica figured in PI. VII, fig. 14, in which the inner wall 

 has covered a number of undeveloped zooecia and heterozooecia I have found an- 

 other small ooecium of the same species in which the corresponding individuals 

 are provided with completely developed apertures. Also the gonozooecium the 

 larger part of which is seen proximally to the tail-shaped process of the ooecium 

 is provided with a completely developed aperture. A third different case I have 

 found in a number of open ooecia belonging to the same species, all of which 

 were placed not far from the growing edge in a superficial layer of growth (pi. VII, 

 fig. 17). Here there projects in the proximal part of the ooecium a number of 

 zooecia and heterozooecia of very différent development while the rest of the inner 

 wall presents a uniform smooth surface, the dissolution of which by the use of 

 diluted acid denudes a layer of completely developed zooecia and heterozooecia 

 belonging to an older part of the colony. In the ooecium figured in PI. VII, fig. 17 

 there is seen in the proximal part a number of open zooecial areas, and the gono- 

 zooecium is in the same state of development, while that figured in fig. 18 shows 

 a number of almost completely developed zooecia and heterozooecia. Proximally 

 to the latter is seen a small triangularly rounded aperture, but the tail-shaped pro- 

 cess seems to have been broken ofT. 



By the aid of the above facts we may form the following picture of the devel- 

 opment of the ooecia. When the gonozooecium begins to expand into the ooecium 

 the inner wall of the latter covers a number of more or less developed zooids, 

 which of course get chequed in their development while the adjacent zooids are 

 able to continue their growth, which explains that the lateral margins of the ooecia 

 are partly covered by a number of zooecia and heterozooecia. When the gono- 

 zooecium belongs to a superficial layer of growth and is placed near to the growing 

 edge, the ooecium first covers the undeveloped zooids placed distally to the gono- 

 zooecium and thereafter a number of zooids belonging to the older part of the 

 colony. The presence of freely prominent zooids in the proximal part of the 

 ooeciuni must no doubt be explained in that manner that they have originally been 

 covered by a bulging part of the inner wall of the ooecium, which has later been 

 destroyed. A curious fact is the difTerent state of development shown by the gono- 

 zooecia even in the same species. 



The aperture of the ooeciuni leads into a short atrium partially divided 

 from the rest of the ooecial cavity by a low ring-shaped ridge (pi. VII, figs. 21, 

 22, 28, 29) which from the inner wall passes obliquely forwards to the frontal 

 wall. By the use of a great magnifying power its surface is seen to be provided 

 with small projections which stand out as free irregular teeth on its distal mar- 

 gin (pi. VII, fig. 28). Harmer ') has pointed out a similar atrium in the ooecia of 



') 12 a, p. 170, pi. XII, fig. 10. 



