NOVEMBER 5, 1897. ] 
d. Fusion of the anterior piece of one larva 
with the ventral side of another. 
e. Fusion of two posterior pieces. 
f. Fusion of the heads of two larvee. 
g. Fusion of anterior pieces. 
2. The larvze belong to different species or 
even genera. 
a. Fusion of the ventral surfaces. 
b. Fusion of the posterior piece of one 
larva with the ventral surface of the 
other. 
ce. Fusion of an anterior with a posterior 
piece. , 
d. Fusion of the heads of two larvee. 
Every one of these unions was repeated many 
times, and the monograph presents an exact 
description of the anatomical condition of sev- 
eral specimens of each form of double larva, 
after the development had continued some 
weeks. These descriptions are based upon the 
examination of serial sections, the specimens 
being sacrificed on the microtomie altar. It is 
not using too strong a word to characterize the 
labor involyed as enormous. The work, more- 
over, bears throughout the stamp of extreme 
conscientiousness. 
It is impossible to enter here into details, but 
some of the general conclusions formulated by 
the author are so interesting that they are here 
presented. If, by the fusion, corresponding or- 
gans or their anlages are brought into contact 
they unite continuously by the conerescence of 
the specific tissue of the organ (the process 
might be appropriately named ‘ Histofusion,’ 
Rev.). If the anlages of unlike organs are 
brought in contact they become united by con- 
nective tissue. If the similar organs are hollow 
not only do their walls fuse, but also smooth 
open communication of their cavities is estab- 
lished, and in such cases it is not necessary 
that parts precisely corresponding should be 
-joined. The different parts of the digestive 
tube will fuse, or the spinal cord will unite with 
the brain, and there will be produced a smooth 
passage from the cavity of one to that of the 
other, similarly in cases of fusion of the abdomi- 
nal, pericardial or vascular cavities, of hearts, 
wolffian ducts, etc. Tissues are found united 
in this way which at the time of the union were 
still undifferentiated. Under certain conditions 
SCIENCE. 
705 
ectodermal and entodermal epithelia may be- 
come connected. The notochord takes an ex- 
ceptional position in that the notochord of one 
piece does not concresce with that of another. 
The growing together of similar organs or 
tissues may occur in any plane or direction ; 
there is no trace of polarity in the growth, such 
as Vochting records for plants. The union of 
two pieces may be not only anatomical, but also 
physiological, and Born designates this as physi- 
ological symbiosis. It occurs in various degrees. 
In probably all cases the blood vessels are in 
open communication, so that the circulation is 
common to both components. A higher degree 
of symbiosis is marked in the cases where the 
intestine of the major larva has annexed a 
piece of the intestine of the minor, and both 
function together to the common advantage, or 
when the two larve have a stretch of intestine 
incommon. The highest degree is reached when 
a whole end of the body, together with all its 
organs, is replaced, lengthened or doubled, for 
then the posterior piece from one larya works 
with the anterior piece of another, as if they 
were one individual. The highest degree is 
equally attained when the right and left halves 
of two larvze are united in a single individual. 
The ‘individuum’ is not dependent on the deri- 
vation from one egg. We have a single organ- 
ism from two eggs (einen einheitlichen organ- 
ismus aus zwei eiern). In the derivation from 
a single oyum there is no mystic, metaphysical 
unity. 
The development, from the stage at which the 
experiments begin, depends upon self-differ- 
entiation of the single parts. No correlative in- 
fluence of the surrounding parts can be recog- 
nized ; the development is mosaic—Feis’ organic 
areas (organbildende Keimbezirke) are partitioned 
off. 
We commend this work to the attention of 
all biologists, and venture to predict that further 
important deductions will be garnered from 
these experiments of Professor Born, supple- 
mented as they soon will be by additional 
researches. CHARLES S. MINOT. 
The Concise Knowledge Library: Natural History. 
By R. LyDEKKER, W. F. Kirpy, B. B. 
WooDWARD, R. KIRKPATRICK, R. I. Pocock, 
