92 _ THE AUSTRALIAN NATURALIST. 
tail-fin is set horizontally. The other ‘‘fins’’ are the pec- 
- toral flippers, and the dorsal fin. The latter is practically 
only an extension of the skinny integument, and it not 
pessessed by all species, (e.g., the Right Whales), but in 
‘some (e.g., the ‘“Killers’’) is very high, indeed. The pec- 
toral flippers are homologous with the arms or fore-legs of 
the terrestrial mammals; and, undoubtedly, all Whale 
‘forms are of terrestrial origin. — - 
The Cetaceans are divided into Whalebone Whales 
(Mystacoceti) and Toothed Whales (Odontocett). The 
largest existing species belong to the former group, but in 
both groups are to be found Whales which are commercially 
sought. 
The Whalebone Whales receive their common name 
because of the presence of large numbers of laminae, or- 
plates of baleen or ‘‘whalebone,’’ which depend into the 
mouth from the upper jaw. These baleen plates vary 
ereatly in number in the different species, reaching as high 
as 400 sheets to the side in the Greenland Whale. In 
length, likewise, there is the greatest variation—in the large 
commercial whales, ranging from 18 inches up to as much 
as 15 feet (the latter representing the length of the longest 
Greenland Whale baleen), while in texture re as has been 
seen, there is very great diversity, 
The baleen plates, which are relatively very thin, are 
set regularly close together, but not touching each other, 
so that a free passage is left between for the water, while 
the feeding process is going on. The bases of the plates 
are wide; and from here they taper regularly all the way 
to the lowermost point. The outer edges of the baleen are 
more or less straight, and quite smooth; but internally, the 
fibres of which they are composed are frayed out or frim- 
piated, so as to present an even hairy surface over the whole 
of the inside of the upper part of the mouth, except the 
palate, which is of a beautiful soft smoothness. These 
frayed-out ends of baleen make an exceedingly efficient 
hair-sieve, which is used in the manner to be described. 
First let me point out, however, that the bases of all the 
baleen plates are set obliquely, so that the inner edge is. 
‘well ahead of the outer—roughly, as the gills of a fish ara 
 set—so as to expedite the passage of water. <A study of 
these shows, in fact, that were they set otherwise, the oper 
