734 



SCIENCE 



[N. S. Vol. XXV. No. 645 



nature. Professor Duerden's argument is 

 not conclusive because he has not yet shown 

 in what way a tetrameral plan of growth 

 shown in the early condition of certain 

 individuals can be in all cases the result 

 of imperfect silicification. The possibility 

 of acceleration is not denied and the very 

 species that he studied show strong evi- 

 dences of acceleration in development. 

 Hence the uncertainty of reasoning from 

 sections, about which there must always be 

 a good deal of doubt. 



Early Stages in Streptelasma and Allied 

 Genera: Thomas C. Brown, Columbia 

 University. 



This paper considers an argument con- 

 cerning the original tetrameral arrange- 

 ment of the septse in Streptelasma and 

 allied genera of the rugose corals and 

 describes the protheca as observed in these 

 genera. 



Fission in the Hydroid Corymorpha: 



Harey Beal Toreey, University of 



California. 



Spontaneous fission occurs occasionally 

 in Corymorpha, across heteromorphie 

 stems. The latter are geotropic, both ends 

 turning upward, and take the form of U's, 

 attached at the loop, with free vertical 

 limbs. The distal limb is the longer, with 

 the larger and earlier hydranth. 



The fission plane is first defined by a con- 

 striction in the loop of the U. The stem 

 attenuates in this region, owing to the 

 migration of proximal and distal limbs 

 away from each other. The coenosarcal 

 canals are obliterated and the circulation 

 characteristic of the stem ceases. This 

 may be the cause of the disintegration 

 which may appear here. Frustules arise 

 on both sides of the constriction before 

 fission is completed. 



The new polyps, proximal and distal, are 

 normal in all respects. Morphallaxis plays 



an important role in their complete de- 

 velopment. 



Variation during the Life-Cycle of In- 

 fusoria in its Bearings on the Determina- 

 tion of Species: Lorande Loss Wood- 

 ruff, Williams College. 

 The data summarized, derived from the 

 culture of various infusoria through long 

 periods, suggest that it is customary to re- 

 gard the structure most frequently ob- 

 served in 'wild' Infusoria as too constant 

 in character, and to overlook the fact that 

 modifications occur throughout the life- 

 cycle which are in no sense abnormal, and 

 which must be taken into account in the 

 determination of species. 



1. Oxytricha fallax, for example, shows 

 a variation of over 250 per cent, in length, 

 and over 300 per cent, in width during the 

 life-cycle. 



2. The shape of the animal changes i 

 greatly at different periods of the life- 

 cycle. 



3. The form of the macronucleus alters 

 exceedingly, not only toward the end of the 

 life-cycle but also at periods of the highest 

 reproductive activity. Peculiarities in 

 shape are sometimes transmitted from 

 generation to generation. During a cycle 

 extending over about a year, the macro- 

 nucleus was 'normal' in form for less than 

 three months. 



4. The number of micronuclei varies 

 during the life-cycle. There is apparently 

 a tendency toward numerical reduction 

 during the early part of the cycle, and 

 reduplication during the latter part. 



5. The quantitative relation of cyto- 

 plasmic and nuclear material changes 

 during the life-cycle. This is brought 

 about by both cytoplasmic, and macro- 

 nuclear and micronuclear changes. 



6. The proportionate length of the 

 ciliary apparatus varies, the cilia being 

 longer during high reproductive periods of 



