MICHIGAN ACADEMY OF SCIENCE. 87 



The preliminary experiments referred to were in the nature of crush- 

 ing the otocyst organs and also ])unctiniug the otoeyst vesicles think- 

 ing thus to put the organs out of function. Although the otocyst organs 

 were very much mutilated the animal behaved better than could be 

 expected. But this was interpreted as showing that the organs were 

 not rendered ineffective. After many experiments which aimed to in- 

 capacitate these organs, it was found that they could be cut away with 

 a portion of the margin, leaving small portions between for the attach- 

 ment of the velum. After the velum was again grown to the bell all 

 around, the remaining portions of the margin were removed in the same 

 way until microscopic examination revealed no more organs present. 

 Repeated trials convinced me that the jellyfish could swim normally 

 after removal of the otocyst organs, showing that these are not essen- 

 tial. Injuries or imperfections of a considerable nature in the velum, 

 the principal muscular organ of locomotion, caused greater disturb- 

 ances in the swimming movements, and led me to believe that the 

 orientation of these animals is more largely in the muscular sensation.^ 



These results induced me to examine the behavior in a few crasta- 

 ceae in Avliich orientation has been found to be wholly due to otocyst 

 organs. The well-known experiment of Kreidl was repeated. It will be 

 remembered that in this experiment the shrimp Palaemonetes, in 

 a freshly moulted condition is placed in filtered sea water to which 

 some iron-filings are added. It is indeed a fascinating sight when the 

 animal repeatedly thrusts all the iron-filings that it can hold Avith its 

 second chelaepeds into the space between the rostrum and the anteu- 

 nules. Sometimes the filings were dropped on the antennules with a 

 pipette, and in this and the former case the chelaepeds were used as 

 if rubbing the filings into the otocysts. Yet the process was so long 

 continued before the animal responded to the magnet that the entrance 

 of any particles into the otocysts seemed rather accidental. A 680 

 windings primary coil with half-inch core of soft iron wires and six 

 cell dry battery were used. It was found that two cells were enough 

 when the animal Avas moving. While stationary, or braced in an angle 

 of the containing vessel, the animal could not easily be disturbed and 

 soon seemed to get used to the pull of the magnet. Normally it responded 

 by bracing against the pull of the magnet, and in one case, even, lying 

 on its side Avith ventre directed tOAvard the magnet. In some cases, how- 

 ever, it was apparently pulled OA^er with the dorsal side toward the 

 magnet. It Avill be seen that this is a result that Prentiss- did not get. 

 If the circuit is made suddenly, Avhile the animal is swimming, it some- 

 times SAvims spirally a turn or two. 



Now there is no doubt that the animal feels a pull and he takes 

 up a natural attitude toward this pull. From considerable observation 

 on the habits of Palaemonetes I haA^e concluded that presenting the 

 A'entral side of the body is a natural attitude of defense against their 

 mates and enemies. I believe it is the pull of the magnet on the iron 

 that makes the animals uncomfortable to the extent of defending them- 

 seh'es and thus turning against the direction of the pull.^ 



While I do not think that these considerations disprove the static 

 function of otocyst organs, I do ihink that Kreidl's experiment is open 



'The results of these experiments were published in Am. Jour. Physiol. Vol. X No. IV. p. 201. 

 ^Bulletin of the Mus. of Comp. Zoology, Harvard University, 1901. 



