ON DTPLOZOON XIPPONICUM, X. SP. 160 



well-stained protoplasm, of a polyhedral form, and leavino- irregular 

 intercellular spaces between (Fig. 14). 



In Axme, the mesenchyma is distinctly seen to consist of laro-e, 

 vesicular cells, each with a nucleus generally in the centre, but some- 

 times attached to the wall, and filled with a hyaline fluid containing 

 numerous almost uncolored granules. The nucleus as in Diplozoon, 

 has a distinct membrane, and encloses a deeply stained nucleolus, but 

 is considerably smaller. Beside these cells, there are, as Lorenz^' has 

 already observed, in the neighbourhood of the vagina, cells whose con- 

 tents take up the staining finid very eagerly and appear like ganglion 

 cells. In MicroGOtyle, the mesenchyma presents somewhat different 

 aspects in ditferent parts of the body — a statement that holds good 

 to a greater or less extent in all other allied forms. Around and 

 outside the vitelline body, the mesenchyma presents an appearance very 

 similar to that of Diplozoon. Nearer the median line, it consists of 

 large cells with tlie nuclei in tlie centre, from which protoplasmic fibres 

 radiate to the wall, whose cavity is filled with a clear fluid without any 

 granule. Along the median line, finally, the mesenchyma consists of 

 cells with a granular somewhat fibrous protoplasm which deeply stains 

 with haematoxylin.-* Here in Microcotijle, I believe, are manifested 

 the transitional steps tlirough which the mesenchymatous connective 

 tissue such as that of Diplozoon has been differentiated from the 

 primitive parenchyma cells. These primitive cells are, I believe, very 

 nearly represented by the cells of the median portion of Microcotijle. 

 The next step onward toward the differentiation of connective tissue 

 is, according to my view, represented by such a form of mesenchyma 

 as that of Axine, or that portion of the same in Microcotylc situated just 

 inside the vitelline body — composed of cells of a vesicular appearance 



1) Loreaz — 1. c. p. 7. 



2) In appearance, these cells are very similar to the yolk-cells of Diplozoon during the 

 wiutor season. Vide. Fig. 20, PI. XXTl. 



