MUSEUM OF COMPARATIVE ZOOLOGY. 113 
fact, that in the anterior trunk region this cord gradually diminishes, 
and then disappears. 
Wenckebach (’84, p. 235) observed the intermediate cell-mass in Perca 
fluviatilis. He did not observe its origin, but described it as a solid mass 
of tissue, situated in the region where afterwards the vena vertebralis is 
found. This structure is regarded by Wenckebach as the source of the 
blood corpuscles. The cells composing the axial portion of this cylin- 
drical mass gradually become detached from one another, and are carried 
away by the plasma which appears at this time ; they acquire a yellow 
tint, and become the blood corpuscles. These conclusions were reached 
independently of Ziegler’s ('82) previous observations on the same struc- 
ture in the Salmon. In a more recent paper Wenckebach (86, p. 246) 
maintains that in Belone acus the intermediate cell-mass arises as a 
single cord of cells below the chorda, and not as two lateral ones which 
later unite, as in case of the Salmon, according to Ziegler (82), and in 
the Brook Trout, according to Oellacher (73). As to the method of its 
origin in Belone acus, the author believes that in an embryo of seventeen 
days individual cells are set free from the mesoblastic somites, and pass 
between the chorda and intestinal canal, and in this place undergo pro- 
liferation until a massive solid cord of cells is produced, which consti- 
tutes the intermediate cell-mass. 
In a more recent paper Ziegler (’87) has discussed quite fully the fate 
of the intermediate cell-mass and its relation to his formative tissue, 
* Bildungsgewebe.” The latter corresponds in gene ral to Hertwig’s 
“Mesenchyme.” Ziegler assigns to it a comprehensive meaning. Ac- 
cording to his use of the term, Bildungsgewebe embraces a wide range 
of tissues of various origin, which in distinction from epithelial tissue 
consist of cells more or less independent of histological connection with 
one another, or connected only by means of delicate processes ; in other 
words, the term includes all mesodermic primitive connective tissue, 
including the blood corpuscles. The use of the term enables the 
author to make a simple general classification of the mesoderm in Verte- 
brates, viz. (1) the muscle-plates, (2) lateral layers, and (3) formative 
tissue. 
The formative tissue, which arises in later stages, is, according to 
Ziegler's view, chiefly formed from the lower, hinder margins of the 
protovertebro. He is inclined to believe that the intermediate cell- 
mass also may yet be shown to be in histological connection with 
the protovertebrie, and hence prefers not to separate intermediate cell- 
mass and formative tissue. At the same time this observer regards the 
