MICHIGAN ACADEMY OF SCIENCE. 77 



the nervous elements of Actiniae, thereby strengthening the results of the 

 Hertwigs. In young specimens of Metridium dianthus he demonstrates 

 uni-, bi-, and multi-polar sensory cells, having fine prolongations which 

 often constitute thin layers of nerve fibrils. On these fibrils are also small 

 cells which are probably sensory cells in different stages of growth. 

 Near these sensory fibrils are other nerve cells of larger size, the motor 

 cells, which are usuaUy multipolar, Havet found these nerve elements 

 in the endoderm and mesogloea as well as in the ectoderm. Besides a 

 nerve layer in the column wall a high degree of nervous development ap- 

 peared in the septa, oesophagus and tentacles. 



From the evidences we now have, it would seem that development of 

 nervous elements among the Anthozoa is rather a matter of degree, vary- 

 ing much in individual species. Where a well defined nerve layer is 

 present, it is a special development of such nerve elements as are always 

 present, and manifestly can have but little phylogenetic or systematic 

 importance. 



University of Michigan. 



SOME RESULTS OF A STUDY OF VARIATION IN PARAMECIUM.^ 



RAYMOND PEARL AND FRANCES J. DUNBAR. 



( Preliminary Communication.) 



1. The results here set forth form a small part of those which have 

 been obtained in a quantitative study of variation and correlation in 

 Paramecia reared under definite and controlled cultural conditions. 

 The purpose with which the work was undertaken was to determine as 

 exactly as possible the eft'ect of a measured environmental change on 

 the degree of the correlation existing between length and breadth of 

 body in this form. Incidentally, of course, the variation exhibited by 

 the individuals in the different cultures was studied. We shall deal 

 here solely with some of the results regarding variation. 



The plan on which the experiments to be considered in this paper 

 were carried out was in outline as follows :" a "standard" culture 

 solution was made by putting 30 gr. of finely chopped hay into a litre 

 of water, heating to 90° C. and straining the infusion through cheese 

 cloth. Then a single individual (not an ex-conjugant) was isolated 

 from a flourishing '"wild" culture of Paramecium and transferred to 

 .^ome of this ''standard" medium. Multiplication then went on until finally 

 we had a well developed culture containing only iudkiduaJi^ ichich were 

 descendants of the original single ancestor. In other words we had in 

 such a culture a single '•'fraternity" of the closest possible degree of 

 selection of original ancestry. Then from this culture experiments 

 were set up in homoeopathic vials. For each experiment three vials 

 were filled to a certain point with culture fluid containing the 

 Paramecia. One of the three vials (A) served as a control, and was 



'Contributions from the Zoological Laboratory, University of Michigan, No. 99. 

 -A detailed account of the experimental methods, making of the measurements, etc., will be given 

 in the complete report of this work. Space is lacking for more than an outline here. 



