BREED: METAMORPHOSIS OF THE MUSCLES OF A BEETLE. 331 
in flexor processus postero-lateralis metafurcae, the muscle next to be 
described. This bend is caused by the presence of a large trachea, a 
branch from the trunk arising at the first abdominal stigma. The tra- 
chea lies in such a position that the muscles are bent around it when 
their ventral attachments shift posteriorly. In older pupae the relations 
of these parts become readjusted so that there is no bend in the muscles. 
The metafurca commences to form very early in the pupa, and by its 
ingrowth carries in the ventral attachments of this muscle, together with 
that of several other muscles. On account of the ingrowth, this muscle 
is shortened in later pupal life until, in the zmago (Plate 5, Figure 11, 
dep. trg.), 1t has about one third of its original length. The attach- 
ments are, dorsally, to the suture between metathorax and abdomen, the 
same as in the larva, and, ventrally, to the tip of the posterior lateral 
horn of the metafurca (méfur. 2). 
The depressor of the tergum is frequently fused with the muscle next 
to be described, this being the case in Bruchus and Colymbetes. This 
condition is probably found in Dytiscus, though Luks does not figure 
either of the muscles. 
Flexor processus postero-lateralis metafurcae. 
(Fléchisseur latéral de lapophyse épisternale postériewre of Straus- 
Diirckheim.) 
This muscle in the larva (Plate 1, Figure 3, flz. pre. p-l. mtfur.) has 
a position exactly parallel with that of the muscle last described, but is 
shorter, lying more laterally. During pupal life (Plate 3, Figure 7, jlx. 
pre. p-l. m?fur.) there is an ingrowth of the hypodermis at both dorsal 
and ventral attachments, so that in the zmago (Plate 5, Figure 11, flz. 
pre. p-l. m?fur.) this muscle lies in a horizontal position instead of a 
vertical one as formerly. This change in position is in such a direction 
that the for ner ventral end lies mediad. The process formed ventrally 
is the metafurca, this muscle being attached to its posterior lateral horn 
(mtfur. 2). The lateral attachment is to the inferior process of the meta- 
phragma (pre. if. mt’phg.). 
The flexor of the posterior lateral horn of the metafurca was found by 
Straus-Diirckheim, but not by Luks. It is certain that it is present in 
Dytiscus, however, since it is present in Colymbetes, extending from the 
posterior lateral horn of the metafurca to the inferior part of the meta- 
phragma, there being no inferior process. In Colymbetes, as also in 
Bruchus, the depressor tergi and this muscle are fused, the development 
VOL, XL,— NO. 7 2 
