8 Mr. R. Vallentin on the 



have thought it desirable to give a figure of it in section, so 

 have placed fig. 18 among my illustrations. 



Dr. Hudson (loc. cit.) says, " In Stephanoceros (as in a few 

 other Rotifera) the young (as Ehrenberg conjectured) is 

 occasionally born alive." In all my serial sections of this 

 Rotifer embryos are found in section in the body-cavity in 

 various stages of development. In the case of some they are 

 in a most advanced condition ; the trophi are to all appear- 

 ance fully formed and in a fit state to allow the Rotiferon to 

 lead a separate existence. They do not appear to occupy any 

 definite space in the body-cavity, being, as stated by Dr. 

 Zacharias {Joe. cit.), " thrust hither and thither by the move- 

 ments of the animal." At the same time, however, the fact 

 must not be passed over in silence that the Rotiferon, besides 

 possessing embryos in the body-cavity, also possesses ova 

 within the tube. Unfortunately I have not been successful 

 enough to obtain these latter in section, owing to the tube 

 invariably dissolving during the various treatments the animal 

 has to pass through before it is ready for the microtome. The 

 ovum being simply placed within the cavity of the tube, and 

 not attached to anything, is easily lost. 



] have not as yet been fortunate enough to witness the 

 birth of the embryos ; bearing in mind their large size and 

 the comparative smallness of the cloacal opening, it seems to 

 me most probable that the parents die, and by their death 

 liberate the enclosed embryos. Quite recently 1 have on two 

 occasions found in my small aquarium partially decayed 

 specimens, with two, and in some instances three, embryos 

 within the tube, and swimming therein apparently in a healthy 

 condition. These embryos may, however, have been hatched 

 from those eggs within the tube ; but in one instance there 

 were within the tube two unhatched eggs which also con- 

 tained free embryos. 



In one series of sections I found an ovum that had formed a 

 gastrula by epibole (PI. II. fig. 17). Dr. Zacharias has viewed 

 this in Rotifer vulgaris, but has given no figure of it. The 

 figure I have given was obtained in section of a specimen, so 

 will confirm his remarks. Unfortunately I have been unable 

 to secure any more specimens containing embryos exhibiting 

 the early segmenting stages ; but from those 1 possess more 

 advanced I am inclined to imagine that after segmentation 

 histolysis sets in and rapidly obliterates the previously existing 

 cells. 



Body-cavity. — Mr. Jackson {he. cit.) says, " the ccelome 

 does not extend into it " [the foot]. On reference to figs. 7 

 and 8 it will be noticed that, owing to the mucous cells failing 



