The Migration of Fishes. 49 
clearly neither necessary nor accurate that mackerel should 
perform the migrations ascribed to them by American writers.” 
The migrations of the mackerel are neither proved nor dis- 
proved by special pleadings of this description. 
The spirit of Prof. Hind’s publication is very different. 
He writes from the standpoint of an investigator, and his 
book is an important contribution to our knowledge of the 
habits of fishes in relation to temperature and currents. I 
feel obliged, however, to call attention to a very serious flaw 
in his chief argument against the annual migration of the 
mackerel. In the chapter on the “Relation of the Supposed 
Migratory Movements of Mackerel to Isothermal Line’’* it 
is claimed that a migration to the north in the spring “ pre- 
supposes the movements of bodies of the same great schools 
of mackerel” which are alleged to pass Massachusetts Bay 
from the waters of the coast of Virginia and New Jersey, 
not only through from ten to twelve degrees of latitude, but 
it assumes that they are able to cross in the early summer, 
and frequently before spawning, numerous isothermal lines in 
descending order. He then refers to the article upon the 
Gulf Stream in Petermann’s Mittheilungen for 1870, in which 
the marine isothermals for the different months are shown by 
means of a chart. A table is given showing the isothermals 
for July. That of 68 degs. would touch the coast at Dela- 
ware Bay; that of 63 degs. 5 mins. at Long Island; that of 
59 degs. at Boston; that of 54 degs. 5 mins. at Cape Sable, 
N. S.; that of 50 degs. at Cape Race, and that of 45 degs. 5 
mins, at the Straits of Belle Isle. 
From this he concludes that “a school of fish moving 
rapidly from Delaware Bay to the Straits of Belle Isle, 
would pass in July from a mean temperature of 68 degs. to a 
* Hind, op. cit., Part II., pp. 15-17. 
