284 . W. C. ALLEE 



plainly becomes folded in many places, a process wh'ch may be due to 

 growth. At the same time a new chitinous covering is excreted by the 

 hypodermis. When this is strong enough the old covering splits around 

 the body between the fourth and fifth thoracic segments. Then the 

 hinder part, consisting of the covering of the thoracic segments and 

 their appendages, is shed. Later the process is repeated for the forward 

 part, head, four thoracic segments and their appendages. Twelve to 

 twenty-four hours may intervene between the shedding of the hinder 

 and forward parts. This process usually but not always takes place at 

 night. 



Wege did not find, as did Ost ('06) for Porcellio, any cases of 

 autotomy, although he observed about a hundred animals. 



The discarded covering is very thin and of a milky white 

 color and consists mostly of chitin. The molting process goes on 

 through life. The time interval between molts is usually from 

 eight to thirty days, although over sixty days may elapse. The 

 variation depends upon the age of the animal, temperature of 

 the medium and the time of year. The interval increases with 

 age and with winter, irrespective of the temperature. Wege's 

 observations were carried on from October to the last of Decem- 

 ber in an evenly heated room, yet the interval increased for 

 adults. The effect of temperature was still more marked for 

 the intervals were much longer when the animals were kept in 

 an unheated cellar. 



This description of Wege's is more detailed than that of Zuel- 

 zer ('07). Her account agrees in essential features with that 

 just given except that she observed that one to two days might 

 elapse between the molting of the anterior and posterior parts. 



In my observations on the molting process in Asellus com- 

 munis I have no data to offer regarding the cause of variation 

 in the interval between molts. In the main the process seems 

 to resemble closely that described by Wege for A. aquaticus. 

 However there are a few important exceptions. Thus in Asellus 

 communis either the anterior or posterior part may shed its cov- 

 ering first and as long as four days may elapse between the 

 molting of. the halves. While this is the typical process yet the 

 molting may occur by segments or even parts of a segment may 

 break off and the molt extend over several days. In one in- 

 stance the isopod molted all but the abdominal covering, which 



