52 Bulletin Wisconsin Natural History Society. [Yol. 10, Nos. 1 & 2. 
molting. 
The molting process in amphipods has been described by sev¬ 
eral writers, more recently by Holmes (’oi,A) for Amphithoe 
longimana, and by Smallwood (’03, ’05) for Talorchestia longicor- 
nis and Orchestia palustris. The method of molting in amphipods 
seems to be quite similar in all species. In Hyalella a transverse 
dorsal split occurs usually between the first and second segments 
of the mesosome and extends about half way around the animal; 
this split at times, however, occurs between the head and the first 
mesosomic segment. Previous to this splitting the skin seems to 
loosen from the body. The head is now pulled backward out of 
the hood, and the animal then pulls itself from the loosened body 
cuticle. Occasionally a longitudinal split occurs along either side 
or both sides; this is not usual and when it occurs it is generally 
caused by the extra muscular effort of the animal in withdrawing 
the body from the skin after the head has been freed; in no case 
did I observe it to occur at the beginning of the molt such as 
Hollies (’oi,A) observed in Amphithoe longimana. 
Hyalellcc do not eat their molted skins, a fact which consid¬ 
erably lessens the difficulties in studying their molting. Thirty 
Hyalcllce were isolated during the spring and their molts counted 
twice a day for a period of thirty-five days; during the autumn 
twenty-six others were isolated and observations continued for a 
period of forty days. Most of them were isolated each in a small 
glass dish in which were placed stones, muck and algae to repro¬ 
duce as nearly as possible their natural habitat. Some were iso¬ 
lated without food to determine if possible the effect of lack of 
nutrition upon the time of molting; but results here were not satis¬ 
factory, the animals dying before a sufficient number of observa¬ 
tions could be made. However, as long as the Hyalellce lived 
without food, molting occurred with about the same frequency as 
in nourished animals. Sex or age have little influence upon the 
number of molts. The conclusions in regard to age may not be 
absolutely correct, because, in judging the age of an individual 
relative size was largely the criterion employed. It may be that 
the season of the year affects the rapidity of the molting under 
natural conditions, but it did not influence appreciably the molting 
period of individuals kept in the laboratory. A total of one hun¬ 
dred twenty-five molts, and ninety-one intervals between molts 
