472 



SCIENCE 



[N. S. Vol. XXXI. No. 795 



but that similar or identical environmental con- 

 ditions exist for them in these places, so that they 

 have come to possess in the course of time a struc- 

 ture so similar that they are included in one and 

 the same genus. 

 A Neio Rhahdocoele, Commensal loith Modioltis 



pUcatulus: Edwin Linton, Washington and 



JeflFerson Oollege. (Presented by title.) 



In searching for redise in a lot of mussels at 

 Woods Hole in July last a small worm .2 mm. 

 in length was found by the writer which at first 

 was taken to be a redia with numerous cercarise 

 already active within it. On subsequent dates 

 others were found. They proved to be turbel- 

 larians belonging to the genus Oraffilla. 



The species is viviparous, at least in July and 

 August. 



All stages of development, from the germ cells 

 in the ovary-vitellarium to active ciliated young 

 with black eye specks, may be seen in the same 

 adult worm. There is a singular lack of uni- 

 formity in the details of development, although 

 the outcome as a rule is the development of a 

 pair of young worms within the same egg-mem- 

 brane. 



The worms are active, but move for only a short 

 distance before changing their direction. They 

 tend to move away from the light. 



Their distribution is dependent on local condi- 

 tions. They were not found in mussels which 

 grow on confined coves or marshy places. The 

 best localities for finding them are those which 

 are exposed only at very low tides and where there 

 is rather free tidal movement. 

 The Inadequacy of the Law of Priority, with a 



Suggestion for Relief: J. S. Kingslet, Tufts 



College. 



Characteristics of the Diverse Races of Parame- 

 cium: H. S. Jennings and Geo. T. Haegitt, 

 Johns Hopkins University. 

 Jennings has described the existence of a num- 

 ber of diverse races in Paramecium, differing con- 

 stantly in size. The junior author of the present 

 paper undertook a cytological study of six of 

 these races, in order to determine their relation 

 to the supposed species, Paramecium caudatum 

 and Paramecium aurelia. It was found that two 

 sets of races could be distinguished, one set having 

 two mieronuelei, the other but one. The races 

 with two mieronuelei were all smaller than those 

 with one. The larger races together thus corre- 

 spond with what had before been described as 

 P. caudatum, the smaller races with P. aurelia. 



The two differ also in the size, position and stain- 

 ing relations of the mieronuelei, in ways that 

 correspond to the descriptions of Hertwig and 

 Maupas. But in rare cases specimens of the cau- 

 datum races have two mieronuelei, those of aurelia 

 races but one, thus confirming the observation of 

 Calkins on this point. The races have remained 

 constant in size in the laboratory for between two 

 and three years. They differ from each other 

 (even within the aurelia or caudatum group) not 

 only morphologically, but physiologically, espe- 

 cially in their relation to conjugation. It has not 

 thus far been possible to cause the members of 

 one race to conjugate with those of another. 

 The Pearl Organs of American Minnows in their 



Relation to the Factors of Descent: Jacob 



Reighard, University of Michigan. 



Pearl organs are horny, conical epidermal up- 

 growths which occur in males and are functional 

 only during the short breeding season. Extensive 

 observation of the breeding activities of many 

 species has made known in detail the whole utility 

 of these organs to the species. They serve chiefly 

 to roughen the skin and enable the male to retain 

 his hold of the female during the brief spawning 

 act. 



In form, size and distribution they afford char- 

 acters by which even the species of a subgenus are 

 easily separable. In general the spawning atti- 

 tudes of males of different species are such as to 

 bring their roughened surfaces into contact with 

 the female and a Lamarckian or Darwinian inter- 

 pretation of the origin and differentiation of the 

 pearl organs is thus suggested. Since the num- 

 ber of spawning attitudes is far fewer than the 

 specific distributions of the organs concerned, the 

 one could not have arisen in correlation with the 

 other. From this fact and others it is concluded 

 that the origin and specific distribution of the 

 pearl organs must have come about without refer- 

 ence to utility and through internal forces. Use 

 differences are here superimposed on structural 

 differences in such way that no specific correlation 

 exists between the two. 



The Causes that Determine the Fauna and Flora 

 of the Small Islands of the New England Coast; 

 a Study in Natural Selection: A. E. Veheill, 

 Yale University. 



Abnormal Individuals of Didinium nasutum and 

 their Bearing on the Question of Natural Selec- 

 tion: S. O. Mast, Goucher College, Baltimore. 

 (Presented by title.) 

 In large vessels containing cultures of Didinium 



