ZOOLOGY, ENTOMOLOGY, AND MEDICINE 225 



mum amount required to kill fishes has been made because the 

 determination should be made as the minimum amount for 

 the most sensitive stage in the life history of the fish. This is 

 yet to be investigated. 



Another surprising feature of the investigation is the fact 

 that, while fishes usually turn away from detrimental sub- 

 stances or conditions such as carbondioxide, lack of oxygen, 

 etc., in the case of the poisons thrown into streams by gas 

 plants, they do not avoid the dangerous conditions but swim 

 into them without noting them and on encountering pure 

 water again they very commonly turn back into the poison, 

 though death may ensue there in a short time. This strong 

 tendency on the part of the fish renders the pollution by gas 

 waste many times more dangerous to our supply of fish. 



(A full account of this work will be found in the Bulletin, 

 Illinois State Laboratory, Vol. XI, pp. 381-412.) 



VARIATION INDUCED IN BRACHIOPODS BY EN- 

 VIRONMENTAL CONDITIONS* 



ABSTRACT 



Henry M. Du Bois, University of Illinois 



In order to study the causes of variation in brachiopods, a 

 trip to the San Juan region of Puget Sound was made during 

 the summer of 1915 to study the living forms, their habits of 

 life, and their response to the physical conditions of their en- 

 vironment. Of four species found, Terebratalia obsoleta 

 Sowerby was selected for study on account of its wide distri- 

 bution, i.e., its presence in many habitats. Collections were 

 made from the strand line to 90 fathoms. Complete data 

 were taken as to depth, character of the bottom, exposure to 

 the action of waves and tidal currents, and other physical con- 

 ditions that might have some bearing on the problem. 



The embryonic brachiopods pass through a free-swimming 

 stage which lasts for several days. During this time they are 

 carried about bv the waves and currents and so introduced 



