METHOD OF CELL DIVISION IN MONIEZIA. 153 



micaomeres at the animal pole. 1 The later divisions bring about 

 the formation of a morula which gives off two layers by delamina- 

 tion and then develops into the hexicanth embryo. This cleavage 

 especially in its earlier course differs markedly from that in 

 Tcenia serrata (cf. Janicki's figures with mine). 



As cleavage proceeds many embryos become elongated, a con- 

 dition which Child suggests is due to pressure of the uterine walls. 

 This, of course, does not represent the future axis of elongation. 

 That Child's suggestion is probably the correct one is shown by 

 Moniez's figures from entire embryos which are all spherical 

 and do not include any elongated stages. 



During the early part of my study while I was working upon 

 material in which the results of fixation were good but by no 

 means perfect I thought I had found the syncytial condition of 

 which Child speaks : "In most cases a number of nuclear divisions 

 occur before cell boundaries become visible in the egg. ... As 

 cleavage proceeds the egg is gradually divided into blastomeres 

 containing yolk and blastomeres without yolk. In earlier stages 

 the yolk bearing blastomeres often contain two or more nuclei, 

 but in the later stages after cytoplasmic cleavage is more ad- 

 vanced they usually contain one relatively large nucleus. In 

 other words as these yolk bearing blastomeres are gradually 

 reduced in size by successive cleavages the cytoplasmic cleavages 

 keep pace more nearly with the nuclear divisions. In the yolk- 

 less portion of the egg, however, nuclear division continues far 

 in advance of cytoplasmic division as far as the cleavage has 

 been followed ; the consequence is that each blastomere contains 

 several or many nuclei of relatively small size." 



Later, in studying material in which fixation had been more 

 nearly perfect, I saw at once that the supposed syncytial con- 

 dition was in reality an artifact. From the very first the micro- 

 meres can be distinguished as such, an observation corresponding 

 with the figures of Moniez made about thirty years ago. The 

 cytoplasmic membrane becomes completely constricted even be- 

 fore the telophase is finished as in Fig. 57. In properly fixed 

 material I have never seen an egg syncytium. The work of 



Assuming that, as in all known cases except in the ctenophores according to 

 Korschelt and Heider, the polar bodies indicate the animal pole. 



