MORPHOLOGICAL STUDIES. 
191 
certain exceptions; connected with 1 the cranial ganglia of Ver- 
tebrates above Ichthyopsida, are rudimentary organs which only 
present themselves during embryonic life (Froriep (No. 17), 
Beard (No. 6), Beraneck (No. 10), and Kastschenko (No. 40). 
The explanation so frequently given of such phenomena as 
this, viz. that such organs reappear in the ontogeny as pleasing 
reminiscences of the ancestral forms, if it has any claim to 
pass as an explanation at all, is only a partial one. There are 
many reasons for the reappearance of such rudimentary organs, 
one of which is the part they play in contributing to the for- 
mation of other organs. In fact, to come to the point, we 
are here dealing with cases of Kleinenberg’s law of the de- 
velopment of organs by substitution (No. 41). I will not 
enter at length here into the application of Kleinenberg’s law to 
the nervous system of Vertebrates. For a full comparison of 
the phenomena presented in the development of the Vertebrate 
nervous system with analogous and homologous phenomena in 
that of Annelids (No. 41), our knowledge of the former is as 
yet not sufficient. Some comparisons can even now be made, 
but the time for their consideration had better be deferred. 
The neuro-cpithelia of the rudiments of the branchial sense 
organs appear in the ontogeny of the higher Vertebrates, be- 
cause they contribute certain form elements to the cranial 
ganglia, and very probably also to some, at least, of the sensory 
cranial nerves. 
In the Chick (figs. 90 — 93, 96) such sense-organ rudiments 
are found in connection with the mesocephalic (figs. 90, 93, m.g.), 
trigeminus (figs. 90, 92, 94, v), facial (90, vii), glossopharyngeus 
(figs. 90, 91, ix), and vagus ganglia. In Mammals (sheep em- 
bryos) Froriep (No. 17) has described them in connection with 
the facial, glossopharyngeus, and vagus ganglia. In Mammals 
they have not as yet been described for the mesocephalic and 
1 Tbe exception here has reference to the nose and ear, for both of wbicb 
organs evidence is accumulating for tbe views of tbeir homology with tbe 
sense organs of tbe lateral line which I originally expressed (Nos. 4, 5, 6). I 
believe the organs of taste also arise from such neuroepithelium and wander 
through one, or in some cases perhaps two, gill-clefts on each side into the mouth 
cavity. My evidence for this conclusion will be produced in another Study. 
