304 : Arnold Lang, 
»At this stage of growth, the wall of the heart consists of 
an outer peritoneal cubical epithelium and an inner but indistinct 
endothelium. Between these two layers it is not possible to detect 
any muscular tissue. The cavity of the heart is, however, 
invaded by strands of cells which repeat the struc- 
ture of the heart wall, and are probably invagin- 
ations of it. In A. Grubei the invagination is clearly 
marked, Later on, as the muscular tissue develops in the wall 
of the heart, fresh invaginations occur, composed of an extremely 
delicate endothelium, a muscular layer and a mass of cells, some 
granular, some glandular. forming a fairly definite lining to the 
invagination, but projecting at their free ends into an irregular 
lumen, partially blocked up by cells within which yellowish or 
yellowish-brown granules may be seen.“ 
Aehnlich sind die Verhaltnisse bei Arenicola Grubei. 
Bei 140 mm lJangen Exemplaren 
»the first traces of the heart-body are found as 
a few short and apparently solid ingrowths of the 
muscular and peritoneal layers of the heard wall. 
These ingrowths occur on the posterior (and to some extent outer) 
surface of the heart, where the muscular layer is specially deve- 
loped*. ,The granular chloragogenous bodies are in 
this way carried into the cavity of the heart.“ 
Die Wandung des Herzkérpers zeigt, da er aus einer Ein- 
stiilpung des Herzens hervorgegangen, die umgekehrte Schichten- 
folge der Herzwand, d. h. zu auBSerst ein Endothel, dann die 
Muskelschicht und zu innerst die Peritonealzellen. Bei alteren 
Exemplaren (200 mm) nimmt die Zahl der Einwucherungen von 
der hinteren Herzwand zu. Einige entwickeln sich auch von der 
gegentiberliegenden Wand. 
»ln these the neck of the involutionis hollow, 
showing the nature of the ingrowth, involving, as it 
does, the entire thickness of the wall of the heart 
and a virtual extension fo the coelom into the pro- 
cesses." 
Die Verfasser beschreiben auch kurz die Bildung des Herz- 
kérpers von A. ecaudata, die sich von der bei A. Grubei 
nicht nennenswert unterscheidet. Die Befunde bestitigen also 
Eisias Suggestion, daf der Herzkérper intravasales 
Peritonealgewebe sei. Beziiglich seiner Funktion sagen 
die Verfasser : 
»The heart-body, in fact, appears to be a means of pre- 
venting regurgitation of the blood into the gastric plexus after 
systole, and of ensuring its passage into the ventral vessel.“ 
