443 
as evidence confirmatory to the view that this muscle is not derived 
from myotomic buds, he finds that it is innervated not by ventral 
spinal roots, but by a branch of the vagus (X), to which he gives the 
name ramus recurrens vagi. 
At the suggestion of Prof. von Kuprrer, I have undertaken a 
renewed investigation of the development of this muscle in embryos 
of Petromyzon marinus, as later researches had led him to question 
his earlier interpretation. Before giving the results of my own investig- 
ation, however, it will be well to state the evidence which led 
KUPFFER to conclude that the muscle in question is cutaneous in origin. 
He writes (95, p. 120) as follows: “Bei 5 mm langen Ammocoeten 
sehe ich diese Muskeln zuerst in Form paariger, diinner Strange, deren 
Bestimmung noch nicht zu erkennen ist, hart an der Epidermis, etwas 
lateral von den ventralen Enden der Kiemenknorpel, Fig. 6 mw; die 
Stränge zeigen branchiomere An- und Abschwellungen. Zu gleicher 
Zeit sind hinter dem Kiemendarm die Myomeren bereits in die Ventral- 
region hinabgewachsen, erreichen aber noch nicht die Mittellinie. Etwas 
jüngere Stadien, von 4 mm Länge, enthalten diese dünnen Stränge 
nicht, wohl aber an der gleichen Stelle Wülste der Epidermis mit 
lebhaft proliferirenden Zellen, Fig. 5 mw. Die Stränge lösen sich 
von diesen Wülsten ab. Die weitere Entwickelung zum Muskel erfolgt 
dann rasch, an Exemplaren von 6 mm Länge ist das Organ un- 
verkennbar.” 
In embryos of Petromyzon marinus of 6 mm (13th day of develop- 
ment), I find the relations of the “Bauchmuskel” to be such as KuPFFER 
describes in an embryo of Petr. Planeri of 5 mm. I find however 
in cross sections of this stage that both muscle Anlage and ectodermal 
thickenings are present, the thickenings (Wülste) lying in some sections 
median and ventral and in others lateral and dorsal to the muscles. 
A well marked basal membrane (nembrana prima) separates ecto- 
derm from the muscles. Moreover, although the muscle ends at a 
point posterior to its final anterior termination, nevertheless there is 
no evidence of proliferation of cells from the ectodermal thickening 
anterior to this point, nor does the anterior point of the muscle end 
in the thickening. Also in sections of earlier stage I am unable to 
find a proliferation of cells from the thickening, the membrana 
prima remaining unbroken in all the sections I have examined. 
Having presented this negative evidence that the muscle is not derived 
from ectoderm, I now turn to the consideration of evidence which 
leads me to conclude that it is the product of myotomic buds — there- 
29* 
