476 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
tudinally or by disarticulating the cast somewhere on the dorsal side 
and extricating the body. The most common method is to disarticu¬ 
late the cast at the junction of head and first segment and to creep out 
forward thus causing the anterior end of the cast to crowd together as 
seen in four out of these twelve examples. I have seen one individual 
in the process of casting its cuticle and it proceeded according to this 
method. Healthy individuals cast at intervals of a few weeks in the 
aboratory. 
Locomotion. 
In a species of the millepedes according to Sinclair ( 95 ) the wave¬ 
like motion seemed to pass along the legs moving them in sets of five. 
Lankester ( 03 ) calls this a “swing group,” including in this term 
all those legs in different stages of taking a step between any two legs 
in the same stage. He finds that the change of phase appears from 
behind and passes forward and that the smallest possible “swinggroup” 
(two) was shown in Peripatus, one of six was shown in a Chilopod 
Scolopendra subspinipes, and one of sixteen in the millepede Arckispi- 
rostreptus pyrocephalus. 
Its method of locomotion goes to prove that Scutigerella is Chil- 
ognath-like rather than like a Chilopod. Lankester states that in the 
Diplopods there are symmetrical and identical movements on the two 
sides of the body whereas in the Chilopods, correlated with the lateral 
undulation of the body, the legs 
on the opposite sides of the body 
act in alternating groups. 
Now the “swing group” of 
Scutigerella seems to be three, 
that is, every fourth leg on the 
one side of the body is in the 
same relative position and the 
two sides correspond. The three 
in the swing group have their 
tarsi closely approximated at times so that the threefold mark made 
by the feet looks nearly like one. As the feet are not usually raised 
much but are dragged through the arc when changing position, 
the trail of a Scutigerella is made up of two parallel lines separated 
by the space between the claws (a little greater than the width of the 
body) and marked by opposite three-parted dots, the claw marks. 
