28o OTT. [Vol. VII. 



Wagner ('89, p. 191 ; see page 298), in describing the process 

 of budding in Microstoma, derives the new pharynx from the 

 parenchyme, and also describes a short depression of the integu- 

 ment leading to it. 



I have found that in the budding of Stenostoma leiicops the 

 new pharynx is formed by a process like that described by Wag- 

 ner for Microstoma. (See page 298.) My observations differ 

 from those of Wagner only in this respect, that I find the cone- 

 shaped depression of the integument more pronounced. I 

 know of no other observations on the development of the 

 pharynx in Rhabdocoels. 



Turning to the Polyclads, we find the observations of Goette 

 as quoted above. In addition to these we have those of Lang 

 ('88, p. 166) and Hallez ('79). These observers agree in de- 

 riving the entire pharyngeal apparatus from a depression of the 

 ectoderm. 



Among the Triclads we have the observations of lijima ('84) 

 and Hallez i^Z"]) showing conclusively that the pharynx is 

 derived from the entoderm (mesoderm). 



It has been shown by Wagner for Microstojua and myself 

 for Ste?tostojna that the simple pharynx of the Microstomidae 

 consists of two parts. One of these is formed by an ectodermic 

 depression, and to this I have given, tentatively, the name 

 "cone-shaped depression." The other portion is formed from 

 the parenchyne (mesenchyme), and this I have called "pharynx" 

 in the narrower sense. 



The cone-shaped depression differs from the pharynx in its 

 mode of development, in the character of its epithelial cells, 

 and in the arrangement of its layers of muscle fibres. I believe 

 it to be homologous with the entire pharyngeal apparatus of the 

 Polyclads. 



The portion which I have called the pharynx in Stenostoma 

 leiicops is derived from the parenchyme in the process of bud- 

 ding, and differs from the cone-shaped depression in the manner 

 stated above. 



The parenchyme cells, from which the new pharynx is formed, 

 might be derived by a migration of cells from the adjacent ecto- 

 derm. If this could be shown to be the case, the whole pharyn- 

 geal apparatus (cone-shaped depression and pharynx) of the 

 Microstomidae would be shown to be of ectodermic origin, 



