Mr. T. Davidson on the Brachiopoda. 489 



subject to better understand the position of the muscles than 

 can be made out in Prof. Quenstedt^s diagrammatic figures. Be- 

 fore quitting the subject of the muscles, I may likewise remind 

 the reader, that Mr. Hancock has objected to the hypothesis of 

 " the sliding action oi protractor and retractor muscles;'* he re- 

 gards the decussating muscle as a " compensator for the want of 

 teeth at the hinge ; a means of keeping the valves opposite to 

 each other : " he says, " The valves would appear to be opened 

 somewhat in the manner of the Bryozoa by the aid of fluids. 

 The posterior adductor contracts, the anterior relaxes ; the fluids 

 are pressed forwards, the valves separate. The protrusion of the 

 arms will also help.'* — Hancock, MS. 



The justness of these remarks, at least in Crania, would appear 

 to be confirmed by Mr. Barrett's observation, " that the valve 

 opens by moving upon the straight side, as on a hinge without 

 sliding the valve." 



3. On the Sexes and Ova of the Brachiopoda. 



In the first chapter of the Introduction to my work on the 

 British Fossil Brachiopoda (p. 21), Prof. Owen adds many in- 

 teresting observations he had made on the ''Generative Si/stem'/' 

 it will therefore not be devoid of interest to give here a trans- 

 lation of what Prof. Oscar Schmidt has also published on the 

 same subject*. 



" From his examination of the animal of Terebratula pre- 

 served in spirits of wine. Prof. Owen arrived at the conclusion 

 that the sexes were separate, and lately M. J. Miillerf has 

 brought forward a similar supposition. I had also become 

 certain of this point after my examination of the living Tere- 

 bratula which I obtained in the Oexfjord during my journey to 

 Norway in the summer of 1850, and I have already published 

 these observations in the second edition of my ' Comparative 

 Anatomy,' p. 314, 1852, as well as in p. 295 of my ' Manual 

 of Zoology,' 1854. The sexual glands are found in the mantle, 

 and their shape varies according to individuals (PL X. fig. 9). 

 In the species of Terebratula examined by myself { the testicles 



* *' Die neuesten Untersuchungen iiber die Brachiopoden von Owen, 

 Carpenter und Davidson, mit einigen Zusatzen." (Printed in the Zeitschrift 

 fiir die gesammten Naturwissenschaften, p. 327, pi. Hj 12. May 1854.) 



t " See the reports of the meetings of the Naturforschende Freunde of 

 Berlin." 



X " This species was often obtained by myself in the OexQord, and is 

 not mentioned in Loven's ' Index der Scandinavischen Mollusken.' From 

 the structure of the shell it can hardly be distinguished from the Wald- 

 heimia australis. 



" The TerehratulcB from the septentrional shores of Norway, according 



