BROOKS AND RITTKNHOUSE. On Tumtopsis. 



PLATE 33. 

 The later stages of segmentation, and the planula. 



Fig. 24. The sixteen-celled stage. 



Fig. 25-26. Two more embryos in the same stage, to illustrate the irregular- 

 ity of the segmentation. 



Fig. 27. A more advanced stage of segmentation. 



Fig. 28. An embryo, still more advanced, with an indication of division into 

 two. 



Fig. 29. The division into two is still more marked, only a single cell joining 

 them together. When the two portions are separated artifici- 

 ally at this stage a normal plunula arises from each, and it is 

 probable that the embryos multiply by fission in a state of nature. 



Fig. 30. Another embryo exhibiting division into two parts. 



Fig. 31. The young planula. 



Fig. 32. An older planula beginning to elongate. 



Fig. 33. An older planula, more elongated. 



Fig. 34. A section through the embryo shown in figure 28. 



