494. Miscellaneous. 
even in the canal by which the Main has been connected with a 
confluent of the Danube; so that Dreissena will shortly be an 
inhabitant of the upper and lower portions of the Danube without 
being found in the middle part of its course. 
‘Prof. E. A. Rossmassler, in his popular journal ‘Aus der Heimath,’ 
pp. 71-78 and 347-350, alludes to the same subject, principally its 
first appearance in Northern Germany, and states that the animal is 
able to detach the filaments by which it fixes itself to other objects, 
and that it is frequently found attached to the tail of crayfishes. 
“Dr. Morch (Ueber Pinna fluviatilis (Sander), Malak. Blatt. il 
pp. 110-117) defends his opinion (alluded to in the preceding note), 
viz. that a shell described by Sander in the year 1780 from a rivulet 
near Carlsruhe, is Dreissena, by an analysis of Sander’s account, and 
by the analogous fact that the occurrence of the genus Unio in 
Denmark remained unknown to so careful an observer as O. F. Miller 
(1773). But we cannot accept this as a very convincing argument, 
inasmuch as Unio has been included in all the faunas of the sur- 
rounding countries published at that time (of the Baltic provinces, 
Russia, North Germany, and England) ; whilst Dreissena is not 
mentioned in any of them. 
“Hr. A. Gysser (Mal. Blatt. 1865, Literatur-Blatt, p. 38) also 
discusses this question. He lives at the place indicated by Sander, 
and expresses it as his opinion that the rivulet is a locality unfit for 
Dreissena, that Sander’s shell is a Unio batavus, his description 
entirely agreeing with specimens from that locality, with regard to 
size (two inches) as well as to coloration. A Dreissena of two 
inches would be a great rarity.” 
MISCELLANEOUS. 
Theory of the Skull and the Skeleton. 
To the Editors of the Annals of Natural History. 
GENTLEMEN,—In the ‘ Reader’ newspaper for the 24th of March 
of this year, Mr. Seeley published a letter containing an abstract of 
the paper, then recently read by him, which was published at length 
in the last Number of your Journal. After reading Mr. Seeley’s 
communication, I wrote to the editor of the ‘Reader’ the following 
note, which was published on the 3lst of March :— 
** March 27, 1866. 
«Sir, —If Mr. Seeley will refer to the ‘ British and Foreign Medico- 
Chirurgical Review’ for October 1858, he will find, at the close of a 
criticism on Prof. Owen’s ‘ Archetype and Homologies of the Verte- 
brate Skeleton,’ a brief outline of the theory that the vertebrate 
skeleton is a product of mechanical actions, the effects of which have 
been continually accumulated by inheritance. 
«The doctrine which I had there space to present in general out- 
line only, is more fully worked out in the last number of the ‘ Prin- 
ciples of Biology,’ issued in December 1865. 
* HERBERT SPENCER.” 
