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- 

 bratulidse 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 Discinse 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 setae. 



Some of the Brachiopoda appear to attain their full growth in 

 a single season, and all probably live many j^ears 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 soiftetimes 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 



