1120 General Notes. [ November, 
trichia to the number of a dozen or so opposite each segment, 
In fish embryos the actinotrichia finally have their proximal ends 
drawn together out of their original parallel position under the 
epiblast of the fin-fold, and radiate more or less markedly from 
the point where the muscular process from the mesoblastic somite 
is inserted upon them, the same as the diverging setz in the par- 
apodia of worms. This divergency gives rise to the dichotomous 
character of the bony rays of Teleost fishes, since, as I have 
shown in a previous article, the actinotrichia are the rudiments 
of the permanent osseous, segmented rays of the malacoptery- 
gian type. For these reasons I am very strongly inclined to be- 
* lieve that the parapodia of worms and the fin-folds of fishes are 
very intimately and probably genetically allied to each other. 
Another strong reason for such a belief is that in Sagitta in 
which the transverse septa in the body-cavity have been obliterated, 
as in Chordata, the setz are found, as in fish embryos, lying par- 
allel with each other and in horizontal, lateral, continuous fin-folds. 
This would seem to indicate that Sagitta had descended from a 
worm in which a lateral row of parapodia had gradually become 
fused together serially by their edges so as to form a more OF 
less nearly continuous lateral fold. And I see no reason to doubt 
that a similar longitudinal or serial concrescence of primitively dis- 
tinct metameric finlets may have occurred in the Protochordata, 
and given rise to the median and lateral longitudinal fold from 
which all of the fins develop. The next strong reason for this 
conclusion is that an actual longitudinal concrescence of the 
metameric elements of the paired and unpaired fins of fishes 
actually occurs. This is especially obvious to any one who has 
studied the mode of development of the fins of fishes in which 
extensive longitudinal concrescence has taken place, and of which 
any one who will examine an adult skate may easily satisfy him- 
self. In this form the pelvic and pectoral pairs of fins have been 
formed ofa primitively continuous series of metameric elements, 
as shown by the development. The anterior part of the lateral 
series of metameric elements of the fin-fold in this type are crowd- 
ed together at their bases to form a pectoral, the posterior part of 
the series of elements are in the same manner crowded together 
to form the pelvic fin. In this way it comes about that the rays 
and metameric elements lose their original parallel position with 
respect to each other and become divergent distally, while the 
basal parts of the skeletal series of elements concresce or fuse to 
__ form the compound pro-meso and metapterygial pieces. 
es The lateral fins of fishes I regard as having arisen from the 
serially fused notopodial appendages of a worm-like ancestor, 
the unpaired fins in like manner I regard as having arisen from 
rapodia ; the dorsal median fold from the two lateral rows of 
ia which have concresced on the median line, and the 
from the two rows of notopodia which have in like 
