256 NEW YORK STATE MUSEUM 



after, some mite skins were found, their occupants having disappeared. 

 Many of them had assumed characteristic Hypopus forms, to be 

 described later. 



Forms Assumed by the Mite. 



This Acarid appears to have at least five well-defined forms through 

 which it passes in the process of development or which it can assume 

 under varying conditions. The mites hatch from eggs as minute six- 

 legged creatures, as is commonly stated,* which resemble the adults in 

 all other ways except that they have one pair of legs less. When first 

 discovered, the mites swarmed on portions of the carnation roots, in the 

 more common immature form closely resembling the male, but with shorter 

 hairs and with all the legs similar; males and females were also present. 

 After the mites had been under observation a few days, a stout form of a 

 size nearly equal to that of the female was seen, and in which most of the 

 head Avas concealed. It had quite short legs, and between the posterior pair 

 were six ventral suckers. These stout short-legged ones traveled slowly at 

 first — later they became motionless, extended their legs forward, and as- 

 sumed the typical form of the larger Hypopus (PI. xvi, fig. 9). Sub- 

 sequently a female was discovered with one of these nearly developed 

 larger Hypopi within her body, thus showing the connection between the 

 two forms, but transformation to the Hypopus was arrested January 27 

 by placing the individual in alcohol. The change was probably caused 

 by the poor quality of the food, the mites having fed for a month 

 upon the same bit of decaying root. It would thus appear that this is 

 the Hypopus form of the larger or nearly mature individuals. Possibly 

 this transformation under unfavorable conditions so late in life may be 

 limited to the female. 



The last of January the smaller Hypopus was seen (PI. xvi, fig. 7). 

 Other observers have noted that no Hypopi are to be found until the 

 mites have passed from the six-legged to the eight-legged stage. If such 

 be true, the smaller Hypopi can be developed very shortly after the 

 fourth pair of legs are acquired, as it is usually less than half the size 

 of the other form and smaller than most of the young mites. That the 

 smaller Hypopus is the form assumed by the immature mites is rendered 

 quite certain by the following : January 31st, three of the immature mites 

 were carefully taken — one at a time on a needle point — from the carna- 

 tion root and placed in a clean vial with a fresh l)it of cheese. The vial 



* In this species the smallest examples found possessed eight legs. No eggs were seen at any 

 ■time. It may be viviparous as are Tyroghpfius longio>- and 7'. siro THowakd : in Bull. 4 Neiu 

 -Ser., U. S. Dept. Ag-r., Div . £nt., 1896, p. loi). 



