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BULLETIN OF THE UNITED STATES FISH COMMISSION. 
It will be seen that the chief points of difference between Beard’s account and my 
own are two ; (1) In the Bass the anlage of the lateral line is an elongated sac ; in the 
Salmon it is said to be a cord of cells. (2) In the Bass the anlage divides into the sep- 
arate sense organs during its growth backwards; in the Salmon there is first formed 
a continuous cord, and then special jiarts of it become thickened to form the sense 
organs, the intervening parts disappearing. The formation of a continuous cord may 
easily be looked on as a secondary modification of the method displayed in the Bass: 
the division into separate organs has merely been delayed until the anlage has grown 
all the way back. 
Hoffmann’s (21) account of the development of thelateral line is not so easily brought 
into harmony with my description. According to Hoffmann the lateral nerve develops 
some time before the sense organs. The former arises as a histologically modified cell 
string, which is at first a part of the nervous layer of the ectoderm. The string grad- 
ually moves out of the ectoderm, coming to lie at some distance internal to it, but at 
certain points connection is retained with the nervous stratum. The cells establish- 
ing this connection become the side twigs of the lateral nerve (each leading to a seg- 
mental sense organ). At the point of connection with the side twigs, the cells of the 
nervous layer become histologically modified and form a sense organ. Hoffmann points 
out the difference in the development of the two parts of the lateral line in the follow- 
ing words : 
Zwischen den ersten Anlage des Eamns lat. nerv. Vagi nnd den der SinnesMigel bestekt also nnr 
dieser Untersobied, dass Erstgenaniiter in einem se.hr friihen Entwictlungs-stadium anftritt nnd nicht 
segnientirt sich anlegt, wahrend die Sinneshiigel der Seitenorgane erst in einer viel spiitereu Periode 
der Eutwicklnng, zur Ausbildung komineu nnd gleich vom Anfang an segnientirt sind. 
It seems impossible to reconcile Hoffmann’s description with the development of 
the Bass. For in the latter tlie origin of all the lateral line organs from a single cer- 
vical sac is unmistakable, while according to Hoffmann they arise m situ by local modi- 
fication of the ectoderm. The development of the Bass is so very clear in this respect 
that I do not think Hoffmann’s account can be accejited without confirmation. 
In the Selachians (Beard, L c.) the lateral line anlage consists of a thickened 
stripe of ectoderm, made up of the “primitive branchial sense organs” of the last three 
or four gill slits. This anlage grows backward, plowing its way through the indifferent 
ectoderm and becoming transformed into the lateral nerve and the lateral line proper. 
The exact manner in which the lateral line itself develops has not been worked out very 
satisfactorily. In the main point, though, there is an agreement between the Sela- 
chians, Salmon (Beard, 6), and the Bass : the organs of the lateral line originate as an 
anlage confined to the cervical region. It is difficult to homologize precisely the lateral 
line anlage in the Bass and Selachian, for while in the latter the anlage is composed of 
the sense organs of the last four gill clefts, counting in the rudimentary cleft, in the 
former it lies behind the gill clefts and hence represents only those which have dis- 
appeared. It would thus seem that the anlage in the Teleost contains two less bran- 
chial sense organs than in the Selachian. 
The agreement between the forms mentioned above, as to the origin of the lateral 
line anlage, is strong evidence that Beard’s conception of the lateral line is the true 
one. The lateral line is, for Beard, comparable with a tract of head sense bulbs. The 
latter tract phylogenetically arose by the multiplication of a primitive branchial sense 
