The Histogenesis of Cysticerciis pisiformis. 245 



parenchyma. In correspondence with its simplicity of development, 

 Taenia serrata shows a very simple type of adult structure, the 

 various tissues being- comparatively little differentiated from one 

 another. It is owing largely to this simplicity that the difficulty 

 of distinguishing- the vai'ious tissues from each other has arisen, 

 and in accordance therewith, the very considerable differences of 

 opinion of various authors regarding the structure and homology of 

 these tissues. This confusion has been due in part, moreover, to 

 lack of knowledge concerning the precise method of formation of 

 the tissues and the a priori assumption of various processes of growth 

 based solely on knowledge of the adult structure. 



The presence of an ectoderm and the occurrence of any process 

 of gastrulation in the development of Taenia is extremely doubtful. 

 The lack of a true epithelium and the simple character of its tis- 

 sues and mode of nuclear increase, are probably an expression of 

 the degenerate character of this worm. 



The role of the chromosomes in heredity is entirely lost; the 

 nucleus is probably not a morphological, but a physiological unit; 

 the fate of any cell is determined not by its morphological structure 

 but rather by its physiological environment. 



It gives me pleasure in concluding this paper to acknowledge 

 my indebtedness to Dr. Hexey B. Waed for suggesting this problem 

 to me and for his kindly advice and criticism during my work. 



6. Appendix. 



Since writing the above I have read a series of articles by 

 Child (Child, C. M., 1907, Studies on the relation between amitosis 

 and mitosis, in: Biol. Bull., Vol. 12, No. 2, p. 89—114; No. 3, 

 p. 175—190; No. 4, p. 191—224; Vol. 13, No. 3, p. 138-160; No, 4, 

 p. 165—184). 



In these articles Child has amplified his preliminary account, 

 showing that in certain stages in the development of the sexual 

 cells, mitoses are common. 



In the studies which I am conducting at present on the histo- 

 genesis of the reproductive organs in Taenia serrata, I have verified 

 Child's account in many points, but not in all. In the maturation 

 of the egg I find numerous mitoses with well developed attraction 

 spheres. The number of the chromosomes is inconstant, as is also 



