416 Julia B. Platt 
the two kinds of tissue that make up the continuous and apparently 
homogeneous cartilaginous bar, which extends from the auditory 
capsule to the end of the snout. 
In describing the development of the branchial arches in Triton, 
STÖHR (’80, page 482) tells us that here also an almost entire absence 
of yolk granules is a characteristic indication of the Anlagen of the 
visceral skeleton. STÖHR does not trace the origin of these cells 
so free from yolk, but notices that the other tissues of the head 
equally free from yolk are the brain and the cranial ganglia. In 
Siredon, according to STÖHR (loc. cit. page 490) quantities of yolk 
and pigment granules are found in the Anlagen of the visceral skeleton 
and trabeculae, but in Siredon pigment granules are also found in 
large quantities in the brain and ganglia, although absent in the 
Anlagen of the muscles. This further mark of similarity between 
the brain, the cranial ganglia, and the procartilage of the visceral 
arches, seems to me of interest in view of the fact that the tissues 
so similar have been traced in Necturus to a common origin, the 
ectoderm. 
Sr6ur also calls attention to the difference found in Triton 
between the anterior and posterior part of the trabeculae respecting 
the quantity of yolk granules, and to the fact that cartilage first 
appears in the anterior part of the trabecular Anlagen, and is then 
lost in the neighborhood of the eye-muscles, where yolk granules 
are found, but appears again further back in the tissue that lies at 
the side of the chorda. There seems consequently to be an inter- 
ruption in Triton in the formation of the trabecular cartilage which 
corresponds to the point where, in Necturus, the ectodermic and 
mesodermic tissues of these bars unite. 
Fig. 7, pl. XVII, shows a model of the procartilage in the head 
of an embryo of 15 mm. The model was reconstructed from cross- 
sections, of which five are represented in figs. 7 a—7e chiefly to 
show the position of the trabeculae and basicranial plate, and to 
bring the branchial cartilages into relation to the structures which 
lie above them. The horizontal sections given in figs. 6 a—6e, from 
an embryo of the same length, serve to show the relation of the 
branchial cartilages to one another, to the branchial clefts, and to 
the ventral musculature. 
In Fig. 7, the branchial procartilages are seen from their ventral 
surface. Beneath them lies the basicranial plate ending in the 
trabecular bars, which extend downwards and forwards. The trabecular 
