STRUCTURE AND DEVELOPMENT OF LEPIDOSTEUS. 
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homologous with those of the tail, but are formed by a connecting piece between the 
basal stumps (hsemal processes), which originates as a paired median process of these 
stumps.” 
The incomplete homology between the anterior hsemal arches and the true caudal 
hsemal arches which follow them is exactly what we suggest may be the case in 
Elasmobranchii, and if it be admitted in the one case, we see no reason why it should 
not also be admitted in the other. 
Fig. 3. 
Semi-diagrammatic transverse sections through the first caudal vertebra (A), the last trunk vertebra (B), 
and the two trunk vertebrae in front (C and D), of a Salmon embryo of 2-3 centims. (From 
Gotte.) 
ub., hsemal arch; ub'., haemal process; ub"., rib; c., notochord; a., aorta; v., vein; h., connecting pieces 
between haemal processes; u ., kidney; d., intestine; sp'., haemal spine; to'., muscles. 
If this admission is made, the only ground for not regarding the ribs of Elasmo¬ 
branchii as homologous with those of Ganoids is their different position, and we have 
already attempted to prove that this is not a fundamental point. 
The results of our researches appear to us, then, to leave two alternatives as to the 
ribs of Fishes. One of these, which may be called Gotte’s view, may be thus stated : 
-—The hsemal arches are homologous throughout the Pisces : in Teleostei, Ganoidei, 
and Dipnoi,''' the ribs, placed on the inner face of the body-wall, are serially homo¬ 
logous with the ventral parts of the hsemal arches of the tail ; in Elasmobranchii, on 
the other hand, the ribs are neither serially homologous with the hsemal arches of the 
tail nor homologous with the ribs of Teleostei and Ganoidei, but are outgrowths of 
the hsemal processes into the space between the dorso-lateral and ventro-lateral 
* We find tlie serial homology of the ribs and ventral parts of the hsemal arches to be very clear in 
G-eratodus. Wiedeeshetm states that.it is not clear in Protopterus , although he holds that the facts are in 
favour of this view. 
