526 



SCIENCE. 



[N. S. Vol. XV. No. 379. 



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. 



Degeneration in Paramaecium and so-called 

 ' Rejuvenescence ' ivitliout Conjugation : 

 Gary N. Calkins. 



Two individuals, A and B, of Paramae- 

 cium caudatum, from different sources, 

 were isolated February 1, 1901. These 

 were fed on tAventy-four-hour hay-infusion 

 and the number of divisions recorded at 

 periods of from one to three days through- 

 out the year, one individual being isolated 

 each time. At the present time (December 

 30) A is in the four hundredth and B the 

 three hundred and sixtieth generation, and 

 no conjugation has taken place in the direct 

 line of my cultures. Thus far the experi- 

 ments have yielded the following results : 



1. Parammciiim unqtiestionably passes 

 through more or less regular cycles of activ- 

 ity and weakness. 



2. The period of weakness is preceded by 

 one of greater dividing activity. 



3. The period of weakness ends in death, 

 provided the diet (hay-infusion) remains 

 the same. 



4. Beef-extract restores the weakened 

 functions of growth and division, without 

 conjugation. 



5. Normal conjugation between A and 

 B, if followed by the same diet (hay- 

 infiision), does not restore these weakened 

 activities, but is soon followed by death. 



6. Bxogamous conjugation between wild 

 gametes, and followed by hay-infusion diet, 

 results in normal growth, division and life. 



7. Endogamous conjugation does not dif- 

 fer from exogamous conjugation. The ex- 

 conjugants live and divide normally if fed 

 for a time with beef-extract, but die if fed 

 directly with hay-infusion. 



8. One intracellular effect of beef -extract 

 upon weakened Paramozcium is the forma- 

 tion of ' excretory granules. ' Another is 

 the disintegration of the macronucleus. 



9. A few conclusions to be drawn are: 

 {a) A change of diet is necessary for con- 

 tinued vital activities, (fo) What we may 

 call parthenogenesis, or the development 

 of gametes without fertilization, may be 

 induced by change of diet, (c) Conjuga- 

 tion by itself does not 'rejuvenate.' (d) 

 Conjugation probably has some other sig- 

 nificance than that usually accepted; what 

 this significance may be is not indicated 

 thus far by my experiments. 



Note on Metamerism of the Vertehrate 

 Head: W. A. Locy. 



The Median Bundle of the Olfactory Nerve 

 in Elasmohranchs : "W. A. Locy. 



Fertilization in the Pigeon's Egg: E. H. 



Harper. 



In the pigeon's egg, polyspermy has been 

 found to occur normally. The super- 

 numerary sperm nuclei migrate to the- 

 periphery of the germinal disc and give rise 

 to an accessory cleavage. They differ from 

 the cleavage nuclei in the fact that their 

 rate of division is more rapid ; in being sur- 

 rounded by wide areas of liquefaction; in 

 having a finer chromatin network and more 

 slender and elongated chromosomes; and 

 in possessing one-half the somatic number 

 of chromosomes. In their later history as 

 yolk nuclei they divide amitotically. Never 

 more than one sperm nucleus conjugates 

 with the egg nucleus. 



In the earliest stage of the fertilized egg 

 observed, the egg was within the mouth of 

 the oviduct. The first polar spindle was 

 present and was surrounded by many 

 sperm nuclei. Spermatozoa penetrate the 

 egg most readily within the region occu- 

 pied by the germinal vesicle in the ovarian 

 egg, and the pronuclear phenomena also 

 occur about within the limits of this region. 



