1889.] Zoology. 915 
6. The pars ischio-pubica and the pars scapularis are phyletically the 
oldest portions in their respective girdles. 
7. In the Fishes and Dipnoi (also in Ichthyosaunis) the pars iliaca 
does not reach the vertebrae. 
8. The pars iliaca first reaches the vertebrae when the vertebrate in 
question wholly or partially gives up its swimming existence", and its 
hinder limbs, from being swimming organs, begin to serve as supports. 
From this moment the weight of the body in the pubic region must 
be prevented from sinking, and the strong processes of the ventral 
bones must provide a support for the body weight on the free extremi- 
ties. A similar support is formed in part by the pectoral fins. 
9. A fusion of the partes ischio-pubicae of both sides to form an un- 
paired lamina ischio-pubica as in Dipnoi, Ichthyoidea and Derotrema, 
recurs now and then in the larval stages of the salamanders ; i.e., at a 
time when the tail gives the locomotor impulse. 
10. The old question whether the fishes and Amphibia possess only 
a pars ischiada or also a pars pubica, is to be decided by these later 
views. The pars pubica is not a structure first appearing in the Rep- 
tilia, but is characteristic of the fish and amphibian pelvis. The 
certainty of this lies first in the relations of the nervus obt^ratorius, 
and second in the relationships shown by the embryonic chelonian 
and crocodile pelvis. In these lie the key for the interpretation of the 
urodele pelvis, which is repeated ontogenetically in this reptile. 
11. Not only is the pelvis not composed of one or more pairs of 
ventral ribs, but the parts of the pelvis formerly compared by me with 
such (pars iliaca) are actually the last phylogenetically to appear. 
The Segments of the Vertebrate Head.— Van Wighe has 
recently attacked this problem in the light of the facts afforded by 
Amphioxus. He finds {Anat. Anzeiger, IV., p. 558) that in the adult 
the gill slits extend back to or even beyond the 27th myotome, while 
in early specimens the liver empties in the 13th myotome. He also 
thinks that still earlier specimens would show the liver two segments 
farther in front. Now if the liver be taken to indicate the line be- 
tween the head-gut, and that of the body, it follows that the number 
of segments which in Amphioxus corresponds to the head of the Cran- 
iatas is probably nine and cannot be much greater. Amphioxus also 
affords no difiiculty to the view derived from the ontogeny of the 
sharks that the vagus is a complex of two dorsal nerves. He concludes 
that the skull never consists of metamerically arranged cartilaginous 
elements ; only in the occipital region .behind the vagus is there a 
