NEAL: NERVOUS SYSTEM IN SQUALUS ACANTHIAS. 219 
in S. acanthias. Coggi’s account differs, however, from that of Dohrn 
(90%), who found its relations in Torpedo to be similar to those described 
by Miss Platt (91) for S. acanthias. The relations of the acustico- 
facialis and glossopharyngeus remain unchanged. For a long time 
cellular strands persist, showing the primitive relation of these nerves 
to the constrictions between the encephalomeres IV, V, and VI, re- 
spectively. 
Some important changes in the relations of the neural-crest cells 
appear in the next (48-somite) stage, and are shown in Plate 3, Figure 
17. For the first time, we find ‘ fibrillar” connections of the trigeminus 
Anlage with the neural tube. Protoplasmic or fibrillar processes ex- 
tend from the cells which lie opposite the constriction between enceph- 
alomeres III and IV toward both encephalomeres. It has been stated 
by some investigators (Miss Platt, '91, Locy, ’95), that this nerve has its 
origin from the constriction between the neuromeres. Two main roots 
are differentiated later, an anterior, in relation with encephalomere III 
(the “portio minor”), and a posterior, in relation with encephalomere 
IV (the “portio major”). The nearness of the ganglion cells to the 
brain wall renders it impossible for me to determine in which direction, 
whether toward the brain or toward the ganglion, the fibres are first 
developed. The two chief roots of the trigeminus have been described 
for other Vertebrates. 
The thalamic and trochlearis portions of the trigeminus Anlage are 
now much reduced in size, each retaining connection with the rest of 
the nerve fundament by means of an attenuated protoplasmic fibre. 
The acustico-facialis Anlage has assumed fibrillar connection with enceph- 
alomere V, with which it remains connected until the encephalomere 
disappears. Marshall and Spencer (’81, p. 481, *86, p. 100) have stated 
that in Scyllium “there is an important difference between the fifth and 
seventh nerves, inasmuch as in the former the primary root is lost 
and the secondary alone retained, whilst in the latter both primary and 
secondary roots are retained up to stage N, and indeed . . . through- 
out life. The difference between the roots of the fifth and seventh 
nerves just noticed does not occur in the chick.” They also state that 
in early stages in Scyllium embryos the fifth nerve arises from the brain 
by three distinct roots, but that in later stages only two roots are found. 
Their distinction between primary and secondary nerve “roots” is 
obviously unnecessary, since the only true “roots” are the so called 
secondary ones. Before these are established we have to do with 
neural-crest cells, some of which have been shown to be non-nervous 
