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 tlie 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 imago (Plate 5, Figure 11, 

 dep. trg.), it 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 (mffur. 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. 

 (Flechisseur lateral de Vapophyse episternale posterieure of Straus- 



DUrckheira.) 



This muscle in the larva (Plate 1, Figure 3, Jlx. pre. p-l. mffur.) has 

 a position exactly parallel with that of the muscle last described, but is 

 shorter, lying more laterally. Dnvrng pupal life (Plate 3, Figure 7,Jfx. 

 pre. p-l. mffur.) there is an ingrowth of the hypodermis at both dorsal 

 and ventral attachments, so that in the imago (Plate 5, Figure l\, fix. 

 pre. p-l. mffur.) 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 fo'" ner ventral end lies mediad. The process formed ventrally 

 is the metafurca, this muscle being attached to its posterior lateral horn 

 (mffur. 2). The lateral attachment is to the inferior process of the meta- 

 phragma (jp/-c. if. mfplig.). 



The flexor of the posterior lateral horn of the metafurca was found by 

 Straus-Durckheim, 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 



