150 
T. Davidson — What is a Brackiopod ? 
difficult a subject. I am, bowever, truly happy to state that this 
important inquiry has been most ably and successfully elaborated 
during the last forty years by some of the most distinguished anato- 
mists and naturalists of the period. To such men as Hancock, 1 
Cuvier, 2 Owen, 3 Huxley, 4 Gratiolet, 5 Vogt, 6 Macdonald, 7 King, and 
others, we are indebted for an extensive series of dissections and Obser- 
vation s which have defined, to a very considerable extent, what are the 
true characters of the Brachiopod ; while some important researches 
elaborated by Steenstrup, Lacaze-Duthiers, Morse, Dr. Fritz Müller, 
Oscar Schmidt, McCrady, Kowalevsky, and others, have thrown mucli 
additional light upon the embryology and early stages of the group. 
Some differences in opinion, it is true, have been and are still enter- 
tained with respect to the exact function to be attributed to certain 
parts of the animal ; but on all essential questions there is a pretty 
general agreement. 
Before describing the various parts of the animal, it may be as well 
to mention that the Brachiopods have been divided by Bronn into 
two great groups, termed Apygia and Fleuropygia. Professor King, 
considering these to be inadmissible on certain grounds, substituted 
the name Clistenterata for the first group, on account of its including 
auimals that are destitute of an anal aperture ; and the terrn Treten- 
terata for the second, as it embraces animals provided with this 
opening. The former division contains species which have the valves 
articulated, as Terebratula, Spirifer, Iihynchonella, etc. The latter 
comprise species with non-articulated valves, as Lingula, Discina, 
etc. 8 Some very important modifications in the animal are con- 
nected with these two divisions, especially in what relates to the 
muscular System. 
Acoording to Morse the Brachiopods are reproduced by eggs, 
generally kidney-shaped and irregulär, which are discharged from 
the anterior margin of the shell, and drop just beyond the pallial 
membrane, hanging in clusters from the setas. Some uncertainty 
has prevailed as to whether there is a male and female individual. 
Lacaze-Duthiers and Morse state that the sexes are separate, and 
describe them as such in Thecidium and Terebratulina, and the 
Freneli malacologist goes so far as to suggest that a difference is 
even observable in the shell ; but this point I am unable to deter- 
mine. 
Prof. Morse describes the embryo of Terebratulina with great 
minuteness during its six stages of development. It is divided into 
1 Philosophical Transactions Boyal Society, vol. 148, 1858. 
2 Sur l’animal des Lingules, Bull. Soc. Philomatique de Paris, vol. i., 1797, and 
Sur l’animal de la Lingule anatina, Mdmoirs du Museum, vol. i., 1802. 
3 Transactions of Zool. Soc., vol. i., 1833, and Davidson’s General Introduction 
to British Fossil Brachiopoda, vol. i., 1853. 
4 Annals and Mag. of Nat. History, vol. xiv., 2nd series, 1854. 
5 Journal de Conchyliologie, 1857, 1859, and 1860. 
6 Anatomie der Lingula anaiina, 1845. 
7 On the Physiology of the Pallial sinuses of the Brachiopoda, Transactions of the 
Linnamn Society of London, vol. xxiii., p. 373, 1862. 
8 An instructive note on the primary aivisions of the Brachiopods by T. Gill will 
be fouud in the Annals and Mag. of Natural History, 4th, series, vol. xü., 1873. 
