126 A. RICHARDS. 



"If, his (Child's) observations are to prove his contentions 

 then it must be shown: (i) that the binucleate condition 

 which he finds really depends on a division; (2) that about each 

 of these nuclei a part of the protoplasm is marked off, and (3) 

 that the cells so arising again divide by mitosis and possess the 

 normal number of chromosomes." 



REVIEW OF THE LITERATURE. 



The literature of late histological researches upon the tre- 

 matodes and cestodes deals with the general development of the 

 flat-worm tissues, especially with the cuticle and the paren- 

 chyma. The more recent papers also touch upon the question 

 of the occurrence of amitosis in the life history of the various 

 cells. 



Cestode histology according to this late work presents some 

 very unique features. All investigators who have given the 

 subject their attention seem to concur in the view that tissue 

 growth here differs in character from the usual method of cell 

 multiplication. All agree that karyokinetic figures are not to 

 be found as numerously as in other tissues; some assert their 

 entire absence; while one goes so far as to claim that nuclei arise 

 de novo. On the other hand, some papers make no mention of 

 amitosis, possibly due to the fact that the authors have not 

 interested themselves with the problem. A comparison of the 

 cases in which amitosis occurs is difficult to make because many 

 reports, of thirty or more years ago, previous to the introduction 

 of refined methods of technique, have not been substantiated by 

 later work; but, nevertheless, it is safe to say that in no other 

 group of animals have such unique growth phenomena been found 

 by reputable workers. Granting for the moment that these 

 phenomena have been correctly reported, one is compelled to 

 ask what the relation is between them and the parasitic mode of 

 existence which is universal among cestodes. While as yet there 

 is no basis for speculation even on this relation, the modifications 

 of gross structure due to parasitism are so profound in the ces- 

 todes that one may well be deterred from generalizing from 

 observations of peculiar histological conditions in them. 



Bugge ('02) was the first to note the absence of mitosis in 

 cestode tissues in his work upon the flame cells. 



