RECORDS 67 



Summary of Papers. 



Professor Wilson pointed out that in the analysis of cell- 

 homologies, as in genetic homologies in general, the essential 

 criterion is that of common ancestral descent. Cell-homologies 

 may be merely incidental or secondary to regional homologies 

 of the egg, and, owing to the plasticity of cleavage-forms, may 

 be more modified than other forms of homology, even becom- 

 ing obliterated. It was proposed to denote as eqiiivalent those 

 cells giving rise to homologous structures, irrespective of their 

 origin ; while those cells which are alike in ontogenetic origin 

 and position may, irrespective of their fate, be termed Jiomo- 

 blastic. The term homology is applicable in cleavages of like 

 pattern which have been derived from a common ancestral type, 

 and in which the corresponding cells are both homoblastic and 

 equivalent. When the cells, though homoblastic, wholly 

 change their equivalence, or when the cleavage-pattern itself 

 wholly changes, the original homology disappears. 



Dr. Calkins presented the following results : The experi- 

 ments in cultivating Paraincccunn caiidatinn through long 

 periods seem to indicate that, after continued feeding on the 

 same diet, two originally different lines become so similar in 

 chemical composition that conjugation is practically ineffectual. 

 To illustrate, so-called " wild " conjugations were captured, and 

 the ex-conjugants after separation were treated with the regular 

 culture medium ; 84 per cent, of these continued living. In 

 the regular culture series (now. May 13, in the 567th and 

 523d generation, respectively), out of 48 exogamous ex-conju- 

 gants, only three continued to live, /. e., about 6 per cent.; 

 while of the 32 endogamous ex-conjugants only two continued 

 to live, again about 6 per cent. The high percentage of fertile 

 wild, and the low percentage of fertile cultivated forms give 

 reason for the assumption that after continued treatment with 

 the same diet, the conjugants get no new chemical compound 

 by exchange of nuclei, and therefore no "rejuvenation " takes 

 place. P2xperiments with different kinds of reagents are now 

 in progress to ascertain, if possible, what is needed to make 

 such sterile conjugations fertile. 



