892 "The American Naturalist. [October, 
must, in my judgment, be given up; but this is no reason for 
overlooking, as certain writers have done, the fundamental sig- 
nificance of the distinction drawn between the two primary groups 
of mesodermic tissues. Subsequent research has made only one 
important change necessary, namely, the transfer of smooth mus- 
culature from one group tothe other. In view of this change and of 
the fact that parablast has been used with various other meanings, 
and of the unaptness of His’s names, since we renounce the 
theory they correspond to, it will be well to use exclusively the 
newer terms mesothelium and mesenchyma. 
The parablast theory has been defended by His, 77, and modi- 
fied by him, 78. At present he holds to the distinction originally 
drawn, but is inclined to withdraw his hypothesis of the origin 
of the parablast. A number of writers have agreed with His as 
to the separate peripheral development of the mesenchyma (para- 
blast). Among those may be mentioned Rauber, 30, 37, and 
several authors who have dealt with the development of the 
blood. The most important of the disciples of His is Kollmann, 
who, in a series of articles, 22, 23, 24, 25, has maintained the 
double origin of the mesoderm. Of these papers the most im- 
portant is that on the “Randwulst,” or germinal wall, of the 
structure of which in the chick it gives an excellent description. 
Kollmann regards the germinal wall not as a part of the ento- 
derm, but as a distinct organ composed of segmentation spheres, 
and destined to produce blood-vessels with blood, and probably 
also connective tissue; this peripheral anlage (Randkeim) he 
designates as acroblast, and the single cells derived from it he 
names poreuten. Waldeyer, 42, has accepted the parablast 
theory, but with a modification by which he seeks to reconcile 
conflicting observations. His article is written with charac- 
teristic clearness and exhaustive mastery of the literature, and 
will be found especially valuable by those who wish to pursue 
this subject further. Waldeyer distinguishes between the pri- 
mary and secondary segmentation; the former producing the 
ectoderm, entoderm, and archiblastic mesoderm ; the latter occur- 
ring later, and giving rise to the parablast. This remnant of the 
ovum in holoblastic ova consists of cells; in meroblastic ova of 
hd 
