304 BRACHIOPODA. 
ovaries and testes are placed in the mantle; but in Lingula and 
Discina they occur in the perivisceral chamber. The ova escape 
into the oviducts (regarded by Cuvier and others as hearts), 
which open externally, and have nothing to do with the vascular 
system. In Rynchonella there are four oviducts, but in most, 
if not all the other brachiopods, there are only two. In Tere- 
bratulidee they are divided into two portions, called the auricle 
and ventricle by Professor Owen. Mature eggs have been 
found in large numbers in the perivisceral chamber and in the 
oviducts. Recent Discine often have minute fry attached to 
their valves, and Mr. Suess, of Vienna, has noticed a specimen 
of the fossil Stringocephalus, which contained numerous embryo 
shells. 
As yet we know little respecting the development of the 
Brachiopoda, but in their first stage they are free and able to 
swim about until they meet with a suitable position. It is prob- 
able that in the second stage they all adhere by a byssus, which 
in most instances becomes consolidated, and forms a permanent 
organ of attachment. (Prof. Morse describes the embryo of 
Terebratulina with great minuteness during its six stages of 
development. It is divided into two, three, or four lobes clothed 
with vibratile cilia; and before becoming attached swims or 
whirls head foremost by means of the cilia covering the body.) 
Some of the extinct genera (e. g. Spirifera and Strophomena) 
appear to have become free when adult, or to have fixed them- 
selves by some other means. Four genera, belonging to very 
distinct families, cement themselves to foreign objects by the 
substance of the ventral valve. 
The nervous system exhibits a state of development but little 
superior to what is found in Ascidians. No special organs of 
sense have been detected. The red spots in the mantle, supposed 
by some to be rudimentary eyes and ears, are probably the 
glands situated at the base of the setz. 
Some of the Brachiopoda appear to attain their full growth in 
a single season, and all probably live many years after becoming 
adult. The growth of the valves takes place chiefly at the 
margin; adult shells are more globular than the young, and aged 
specimens still more so. The shell is also thickened by the 
deposit of internal layers, which sometimes entirely fill the beak, 
and every portion of the cavity of the interior which is not 
occupied by the animal, suggesting the notion that the creature 
must have died from the plethoric exercise of the calcifying 
function, converting its shell into a mausoleum, like many of the 
ascidian zoophytes. 
The intimate structure of the shell of the Brachiopoda has 
been investigated by Mr. Morris, Professor King, and more 
