360 MANUAL OF. THE MOLLUSCA. 
Discine often have minute fry attached to their yalves, and Mr. 
Suess, of Vienna, has noticed a specimen of the fossil Stringo- 
cephalus, which contained numerous embryo shells. 
As yet we know little respecting the development of the 
Brachiopoda, but there can be no doubt that in their first stage 
they are free and able to swim about until they meet with a 
suitable position. It is probable that in the second stage they 
all adhere by a byssus, which in most instances becomes con- 
solidated, and forms a permanent organ of attachment. Some 
of the extinct genera (e.g. Spirifera and Strophomena) appear 
to have become free when adult, or to have fixed themselves by 
some other means. Four genera, belonging to very distinct 
families, cement themselves to foreign objects by the substance 
of the ventral valve. 
The neryous 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, sup- 
posed by some to be rudimentary eyes and ears, are probably 
the glands situated at the base of the setze. 
The Lamp-shells are all natives of the sea. They are found 
hanging from the branches of corals, the under sides of shelving 
rocks, and the cavities of other shells. Specimens obtained 
from rocky situations are frequently distorted, and those from 
stony and gravelly beds, where there is motion in the waters, 
have the beak worn, the foramen large, and the ornamental 
_ sculpturing of the valves less sharply finished. On clay beds, as 
in the deep clay strata, they are seldom found; but where the 
bottom consists of calcareous mud they appear to be very 
abundant, mooring themselves to every hard substance on the 
sea-bed, and clustering one upon the other. 
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 eyery 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 cal- 
cifying 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 
recently by Dr. Carpenter; according to this last observer, 
