179 



Eisen ('05, p. 108) characterizes the penial bulb of Fridericia as 

 follows: "The penial bulb of Fridericia is quite characteristic and 

 seems to be of similar structure in all of the species investigated by 

 the author. There is only one kind of cells filling the bulb. These 

 cells all open in the extension of the sperm-duct and along the surface 

 of the bulb; the duct connects with the bulb at the base of the latter 

 and cannot strictly be said to enter the bulb." It is necessary to note 

 that Dr. Eisen refers to those cells which open into the penial lumen 

 ("extension of the sperm-duct") and those which open on to the sur- 

 face of the bulb as one kind of cells in his general statement and in 

 the description of several species he refers to them as different kinds 

 of cells by stating that the bulb in certain species has two kinds of 

 cells. This lack of precision is due to the fact that while in the bulbs 

 studied by him the cells are all similar, in some cases the cells of a 

 bulb open on two different surfaces, and these were unfortunately re- 

 ferred to as two kinds of cells. However, it is evident from his 

 descriptions and figures that all of the species which he studied had 

 bulbs in which the cells were all of one kind. 



The work done by the writer shows that although the penial bulb 

 in Fridericia is uniformly lumbricillid in all respects, it is necessary 

 to make a slight alteration in Eisen's characterization. It was found 

 that the seven species examined by the writer can be divided into two 

 groups : one group composed of tenera, siuia, and oconccnsis, in 

 which the bulb is made up of cells of one kind only, some of which 

 open into the penial lumen and others on the external surface; and 

 the other group composed of agilis, firma, and agricola, in which the 

 bulbs possess two distinct types of cell, one of which occupies the 

 peripheral parts of the bulb, opening either into the penial lumen or 

 on the external surface, and the other composing the interior of the 

 bulb, the cells arranged radially about the penial lumen and opening 

 directly into it. These two types of cell are quite distinct, showing 

 uniform, marked differences in position, shape, size, size of nuclei, 

 and staining reaction. It appears that the structure of the bulb in 

 F. douglasensis represents a transitional stage between the two groups 

 mentioned above, since the inner cells which open into the penial lumen 

 in agilis, finiia, and agricola are represented only by a few scattering 

 cells disposed at irregular intervals between the extensions of the 

 peripheral cells. It is apparent that Eisen's original statement con- 

 cerning the character of the bulb in Fridericia must be so revised 

 that provision is made for the occurrence of two kinds of cells in the 

 penial bulb of certain species ; but otherwise his conclusions are 

 supported. 



