346 ON THE ANATOMY AND DEVELOPMENT OF PYROSOMA 
longitudinal bars are added, until the walls of the branchial sac 
assume their perfect form}. 
As I have explained, the sac-like alimentary tract originally ends 
in a conical point at that extremity which is opposite its oral end ; 
and this cone is connected with the external tunic. In subsequent 
stages the cone remains distinct, being directed at an obtuse angle to 
the rest of the hamal wall of the pharynx, while the cellular bands 
which eventually render the endostyle so conspicuous, cease at its 
base. It, at first, communicates by its widely open base with the 
pharyngeal or branchial cavity; but as development proceeds, it 
becomes narrower, in proportion to the endostyle, and at length is 
represented by that slender backward prolongation of the endostyle 
or ‘endostylic cone’ described at the commencement of this memoir 
and represented in fig. 14. 
The languets do not appear till development has advanced a long 
way ; in fact, in the very young buds there is no room for them, as 
almost all the space between the place of the commencement of the 
cesophagus and the place of the ganglion, is occupied by the aperture 
of communication between the prolongation of the endostylic cone 
and the pharynx. As growth proceeds, the distance between the 
ganglion and the cesophageal aperture gradually increases, both 
absolutely and relatively, and in buds 4th of an inch long, one or two 
small tubercles are visible, projecting from the hypopharyngeal band, 
between the cesophageal aperture and that of the canal which 
traverses the prolongation of the endostylic cone. These gradually 
increase in number, elongate, and assume their adult shape and size 
(figs. 24, 25). 
The figures will sufficiently explain the further changes of form 
undergone by the gastro-intestinal portion of the alimentary canal. 
The hepatic tubular system makes its appearance in such buds as 
that represented in fig. 22,as a minute diverticulum of the stomach, 
which elongates, applies itself to the intestine and ramifies over it. 
Krohn (Z ¢ p. 331) saw it originate in a similar manner in 
Phallusia. 
The heart, similar to that of the adult in form and texture, is 
distinctly discernible in buds not more than ,';th of an inch long, 
attached, in its ordinary position, to the wall of the pharynx, just in 
front of the bend of the intestine, between it and the endostylic 
cone. I have not been able to trace out the first condition of this 
1 Krohn (Z ¢. pp. 324 and 327) states that the stigmata of the embryo Pha//usca make 
their appearance as round apertures ; but he affirms that new ones are added, not only in 
front and behind, but in the neural and heemal sides of the first formed series. 
