196 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 
This is not the place to describe the single muscles of the body, but 
there is one which, I will mention, because its disposition can hardly be 
seen as clearly in any other way but in a section through the abdomen. 
The muscle in question is shown in Fig. C r. to., and may be called the 
M. respiratorius, for it serves to approximate the upper and lower cuti- 
cular arches (Fig. 2 D and V) and so to diminish the capacity of the 
abdomen, hence it is to be concluded that it subserves the act of expira- 
tion. It has a broad attachment to the lower part of the side of the 
dorsal arch (cf. Fig. 2 r. to.) and a narrow insertion into the upper edge 
or rim of the ventral arch. It is surrounded by a network of fibrous 
connective tissue. Graber 256 calls this muscle the "dorso-ventral." In 
the living grasshopper the respiratory movements of the two arches are 
readily seen. 
ORGANS OF CIRCULATION. 
These organs I have not examined with sufficient attention to justify 
the publication of my fragmentary observations. The two most recent 
articles on the heart are by Graber 257 and Dogiel,* 58 both of whom refer to 
the older literature. I wish also to use this occasion to refer to the in- 
vestigations of Graber 259 on the pulsating ventral sinus of insects, and 
the discovery of ganglion cells in the heart of Crustacea by Dogiel 260 and 
Berger. 201 The student should also compare Burger's paper 262 on the so- 
called ventral vessel, which he shows to be really a cord of connective 
tissue surrounding the ventral ganglionic cord. 
CONNECTIVE TISSUE. 
In insects all the internal organs of the body are, so to speak, spun 
around by a web of fibrous and fatty tissue, which extends in the space 
between the outer body wall and the digestive tract, so as to surround 
all the intermediate parts. This is the connective tissue, which also 
acts as carrier or staging of the tracheae. The arrangement of this net- 
work is such that the spaces left between the beams or threads of it form 
a system of lacunar spaces, which serve as channels for the circulation 
by being directly connected with the arteries on the one hand and the 
veins on the other. Indeed it is not improbable that the distinctive 
blood-vessels are nothing more than specialized lacunse of the con- 
nective tissue, so that it would be eminently proper to consider the vas- 
*« Graber: Denkschr. Wien. Akad., Bd. 36, p. 75. 
257 Graber : Ueber den propulsatorischen Apparat der Insecten. Arch., f. mikros. Anat., ix (1873), p. 
129. 
^Dogiel : Anatomie und Physiologie des Herzens der Larve von Corethra plumicomis. Mem. Acad. 
St. Petersb., xxiv, Ho. x (1877). 
259 Graber: Ueber den pulsirenden Baucbsinus der Insecten. Arcb. f. mikros. Anat., xii (1876), p. 
575. 
^Dogiel : De la Structure et des Fonctions du Cceur des Crustacea. Arch. Phys., 1877, p. 401. 
261 Berger : Ueber das Vorkommen von Ganglienzellen im Herzen des Flusskrebse, Vienna, 1877, pub- 
lished by Ceroids Sohn. 
161 Burger, Dionys: tiber das sogenannte Bauchgefass der Lepidopteren, nebst, etc. Niederl. Arch. £ 
Zool., iii (1876), p. 97. 
