There is a tail fin, an anal fin and two dorsal fins, both the latter being situated behind the posterior paired fins.
In the head may be noticed a continuation of the rapid growth of the anterior part.
The mouth has become far more narrow and slit-like; and with many other of the organs of the period commences to approach the form of the adult.
The present and the three preceding stages shew the gradual changes by which the first visceral arch becomes converted into the rudiments of the upper and of the lower jaw. The fact of the conversion was first made known through the investigations of Messrs Parker and Gegenbaur.
O.
In this stage the embryo is very rapidly approaching the form of the adult.
This is especially noticeable in the fins, which project in a manner quite characteristic of the adult fish. The mouth is slit-like, and the openings of the nasal sacs no longer retain their primitive circular outline. The external gills project from all the gill-slits including the spiracle.
P.
The head is rapidly elongating by the growth of the snout, and the divisions of the brain can no longer be seen with distinctness from the exterior, and, with the exception of the head and of the external gills, the embryo almost completely resembles the adult.
Q.