488 JOSEPH STAFFORD, 



nach der Natur des KörperpareDchyms, p. 28—29), from a study of 

 the growth and transformation of Cercariae, writes with decision : "Es 

 repräsentirt meiner Ansicht nach das Material , aus welchem durch 

 Vermehrung und Bildung neuer Elemente, welche sich später in 

 Parenchymzellen umwandeln, eine Vergrösserung des Körpers er- 

 möglicht wird." 



Through many different stages of development of Aspidogaster 

 from the embryo upwards I had followed these cells and had already 

 reached the same conclusion before being aware of the above quoted 

 statements referring to allied forms. That this is the zone where 

 growth and differentiation in the animal begin, I am satisfied. But 

 that the most prominent elements in this region — those hitherto 

 described as subcuticular cells etc. — are the actively dividing elements, 

 or, whether these are already stages in the differentiation to other 

 forms, I am not so sure. The latter seems very probable, for, from 

 their differences of size and shape, the swollen appearance of their 

 nuclei, the presence of a single sphere of paranuclein like those of 

 the inactive parenchyma cells, they bear resemblances to other cells 

 that we know to have become specialized for other purposes than 

 that of reproduction. Besides, between these nests of cells and the 

 muscle layers I have often seen smaller nuclei (Fig. 21 K) with 

 dispersed, granular chromatin, that possess a greater affinity for stains. 

 I have not been able to distinguish cell boundaries for these nuclei 

 that lie crowded together between the larger and more evident elements. 

 These appear to me to be the active, reproducing cells from which 

 modification takes place in two directions — those ele- 

 ments towards the cuticle remaining mostly small and indefinite 

 while those towards the centre of the animal increase rapidly in 

 size and transform into parenchyma cells, glands etc. 



1) Since the completion of my work the publication of Nickerson 

 has come before me. In Stichocotyle he also distinguished larger and 

 smaller nuclei, the latter of which he regards as belonging to muscle 

 fibres. This suggested to me that possibly the small nuclei in question 

 were the same as the small nuclei I had already described in Aspido- 

 gaster and regarded as belonging to the actively dividing subcuticular 

 cells of the region of growth. When studying this question, before I 

 had reached the above stated conclusion, the same thought as expressed 

 by NiCKEBsoN had already occui'ed to me and been discarded. However 

 finding it in print caused me once more to return to my sections for 

 more definite data. The small nuclei as described by Nickerson are 

 not the small nuclei that I refer to. His description tallies with what 



