ON THE DIPr,OCHOKDA. 385 



eggs were discharged direct iuto the water. As the lophophore 

 commenced to coil the eggs were retained for a longer and 

 longer portion of the ontogeny in the shelter of the tentacles. 

 Phoronis australis and Phoronis Buskii form the head 

 of the series in this as in nearly all other features of anatomy 

 and physiology. Thus the eggs and young are found in the 

 tentacles, and as a rule still enveloped in the egg-membrane 

 till as late as the Actinotrocha stage with three pairs of 

 tentacles. 



Segmentation, 



The earliest unsegmented ova are found in the lophophore, 

 which fact militates against the view that fertilisation and 

 part of the segmentation is effected in the coelom of the 

 parent^ as was stated to be the case in the Phoronis 

 examined by Kowalevski (9). Cori (4) has been led to doubt 

 this observation, and I have certainly failed to find either in 

 P. Buskii or P. australis a single ovum undergoing seg- 

 mentation within the ccelom. The ova are perfectly round, 

 and surrounded by a very delicate and pellucid membrane, 

 which usually has a small pedicle by which it was attached 

 to the mucus band (see fig. 20). 



The first segmentation results in the formation of two equal 

 blastomeres, which appear to be almost symmetrical. The 

 second furrow is at right angles to the first, and results in four 

 quadrants which now differ slightly at the two poles. Each 

 tapers to one end, so that the whole egg appears to be slightly 

 pointed and broader at the base (figs. 2 and 3). This condi- 

 tion is foreshadowed in the two-cell stage, but becomes well 

 marked here. A view of the base (fig. 4) shows the arrange- 

 ment in whicli two opposite blastomeres form a cross-line. 

 All the eggs of this and the eight-cell stage whicli I have 

 seen show this arrangement, though, as in the case of the frog, 

 there are probably variations, and the point is one to which 

 little importance need be attached. At the apex the two 

 furrows form a regular cross. A transverse section of this 



