ON BUDDING IN POLYZOA. 545 



equivalent to the embryonic cells (segmentation spheres) of 

 larvae in the blastula stage. Moreover^ the invuginated or 

 grown-over hypoblast cells of the gastrula stage are not 

 derived from the epiblast (ectoderm). Before this difference 

 in position these two layers are usually optically, and they 

 certainly are morphologically and physiologically, quite dis- 

 tinct — apparent optical similarity can never constitute morpho- 

 logical identity. The fundamental difference between the 

 epiblast and the hypoblast is shown by the usually very early 

 distinction between these two layers. For instance, the two 

 layers are often practically distinguishable in the stage of 

 eight segmentation spheres, and even in some cases the first 

 segmentation furrow marks their distinctness. We must, 

 therefore, disallow the use of the term " endoderm " for that 

 mass of cells derived from the epiblast of the parent zooecium, 

 which is supposed to give rise to the alimentary canal of the 

 new polypide. 



We can agree with Salensky when he continues : — " From 

 its position and from the formations which it produces, the 

 inferior layer of the zooecium presents a great resemblance to 

 the mesoderm." He might have added that they are one and 

 the same. 



This method of bud-formation he believes to be common to 

 the whole group of the Polyzoa. 



A. Hyatt, in his elaborate memoir on the ' Sub-order Pliylac- 

 tolsemata' (20), scarcely alludes to the phenomenon of gemma- 

 tion. On p. 221 he says : — " The free part of the endocyst of 

 the cell on the abdominal side, bringing forth true buds.^' 

 And on p. 218 he gives a sketchy account of how "the stato- 

 blastic polypide begins to multiply by the process of budding. 

 An internal swelling of the endocyst, on the lower side, in the 

 vicinity of the bases of the anterior retractor muscles, first 

 shows the position of the coming polypide. This elongates 

 into a little hollow sac with a thickened rim, upon the upper 

 edge of which, in the Hippocrepian Polyzoa, a slight notch is 

 formed by the dui)lication and pushing out of its sides into two 

 loops joined along the centre ^' (the lophophore). . . . '* A 



