EMBRYOLOGY OF THE SEA BASS. 
253 
organ, the multiplication taking place along a line which gradually extended farther 
and farther from its starting point. In the case of the lateral line the phylogenetic 
development has been the same; the sense organs of the last few gill slits instead of 
sending out tracts over the head i>roliferated in a backward direction along the middle 
line of the lateral surface of the body, and so gave rise to a row of organs stretching 
far beyond the region (branchial) to which they were originally conttued. Balfour 
foreshadowed this theory when he suggested (T. B., vol. xi, p. 445) that the develop- 
ment of the anlage in the neck and the innervation of the line by the vagus indicated 
that “ the lateral line was probably originally restricted to the anterior part of the 
body.” 
The homology instituted by Eisig (11) between the lateral line organs of fishes and 
the “ Seiten organe” of certain annelids (Caintellidw) is well known. Balfour in his 
text book declined to accept it, and though Beard favored the homology in his paper 
on the Teleostean lateral line (6), after studying the Selachians he gave it up. Now 
that the early development of the lateral line is approximately known in Teleosts 
and Selachians, there seems less than ever to be said for the homology. If it could 
be shown that the segmental sense organs of annelids, leeches, etc., arise from an 
anterior anlage, which grows back and, so to speak, distributes the sense organs along 
the trunk, the homology might well be supported. But, as far as I know, the inverte- 
brate segmental sense organs arise in sitn. 
Professor Whitman, in a paper on the “Segmental Sense Organs of Leeches” 
(44), supported the homology in 1884, and has recently said (45) that he still regards 
the position as tenable, although aware of the difficulties. Professor Whitman’s 
paper dealing with this iioint will be awaited with a good deal of interest. In the 
mean time one can not but think that the segmental arrangement of the lateral line 
organs in some fishes (Salmon) has been looked at too closely, for in Whitman’s 
account of the leech segmental organs there is found the following passage: “The 
developmental history of these lateral organs in the fish, where they make their first 
appearance as segmental papilla’ in the strictest sense of the words, can not at present be 
explained on a more satisfactory hypothesis” {i. e., hypothesis of homology between 
leech organs and lateral line organs). But in the presence of so many fishes in 
which at the time of hatching there are only a few sense organs to the whole line (see 
Ryder, 34, p. 508), and in which there is consequently no segmental arrangement at 
all, it is obviously unwarranted to assume that fishes like the Salmon present the 
ancestral condition of the lateral line. Further, even if in the Salmon the lateral line 
organs do first make their appearance segmentally arranged, tbe Bass development 
and Beard’s observations make it extremely probable that here also the lateral line 
anlage first forms in the neck and then grows back, xrroducing a continuous long 
cord on which the organs subsequently develop, a method which it seems best to 
look on as a secondary modification of the simple increase by division, which the 
organs undergo in the embryo Bass. 
VIII. ORGANS FORMED FROM THE MESODERM. 
Ccelom, — The lateral mesoderm jdates of the young embryo seen in transverse 
section in Fig. 61, PI. xcv, mes., have a forward extension such as is shown in Fig. 146, 
PI. ovi, som. In front of the plate the mesoderm consists of scattered cells, which in 
