256 Phylum Art hr op oda 



A diagram of a small cage suitable for rearing ticks on guinea pigs, 

 white rats, mice, chipmunks and other small rodents, is shown in Figure 

 58. The wire frame, for keeping the sack in which the cage is enclosed 

 from being gnawed by the caged animal, is soldered to the cage. The 

 cage is placed in a cloth bag, the animal introduced into the cage and the 

 ticks to be fed are placed on the animal. The bag is closely tied and 

 the unit placed over a tray of sawdust. No further attention, except for 

 feeding the animal, is necessary until the ticks have fed and dropped. 

 The fed ticks are recovered from the bag with forceps, and after having 

 been immersed in water to remove the animal urine with which they are 

 likely to have been in contact in the bag, are dried and put away in the 

 usual manner for molting. 



Family hydrachnidae 



PARASITIC WATER MITES 



John H. Welsh, Harvard University 



MOST parasites may be maintained in the laboratory when it is 

 possible to maintain their hosts, and the modifications which many 

 of them exhibit never cease to interest students. Forms which show 

 structural adaptations are numerous but forms which show clear-cut 

 modifications in behavior are few. It would appear to be of interest to 

 know that a form which is readily obtained and maintained in the 

 laboratory does show a striking modification in behavior due to its para- 

 sitic existence. 



Unionicola ypsilophora is a common parasitic water mite which is found 

 in several species of Anodonta. It lives on the gills and all of the develop- 

 mental stages may be found in or on the gills of a form such as Anodonta 

 cataracta. A supply of these mussels may be kept for months in the 

 laboratory in running water and the mites may therefore be available at 

 any time, even though collecting conditions are unfavorable. The mites, 

 after removal from the mussels, may also be maintained in finger bowls 

 of water for several weeks and even months if the temperature is around 

 40-50 F. They require little attention although they may be fed an 

 occasional small bit of mussel gill. 



After these mites have been removed from their host they show a well- 

 marked positive phototropism. This at first seems anomalous as it is 

 difficult to understand why they are not attracted from the mussel, by 

 way of the siphons, when a bright beam of light penetrates the mantle 

 cavity as frequently happens at mid-day. The reason they do not leave 

 the host is seen when the following experiment is performed. If water 

 from the mantle cavity of the host or a filtered water extract of the gills 



