ECARDINBS. 



73 



youngest stage of TerehratuUna septentrionalis strongly recalls the 

 shape of the shell in Megerlia and Argiope. Later, a stage develops 

 which, on account of the long, flattened shell- valves and the long 

 peduncle, strikingly recalls Lingula, and this leads finally to the 

 adult form. 



The only details known as to the development of the inner organs are 

 such as are easily understood. The division of the intestine into sepa- 

 rate sections and 

 the development 

 of the hepatic 

 tubes as lateral 

 diverticula of the 

 anterior section 

 of the intestine 

 <Fig. 35 A, I) are 

 among these, as 

 also the rise of 

 the nervous sys- 

 tem from thick- 

 enings of the 

 ectoderm. The 

 original connec- 

 tion of the cen- 

 tral nervous sys- 

 tem Avith the 

 ectoderm in va- 

 rious forms of 

 the Brachiopoda 

 is, as in Plioronis, 

 retained through- 

 out life. 



Fig. 36. — Lingula larva (after Brooks), a, anus ; d, dilated anterior 

 section of the intestine; d', narrowed terminal section of the 

 same ; e, epistome ; )/!, mouth ; oe, oesophagus ; .s, rudiment of 

 peduncle ; t, unpaired tentacle ; (', youngest tentacle-buds. 



II. Ecardines. 



The embryonic development of the Ecardines is up to the present 

 imknown. Only the pelagic larvae and the youngest attached forms 

 are known, the metamorphosis, briefly noticed by F. Muller and 

 McCrady, having been chiefly investigated by Brooks in Lingula 

 (Xo. 5). The most striking feature in the metamorphosis of this 

 group is, that the pelagic larvae are at a very advanced stage of 

 development which, in the Testicardines, is reached only after 

 attachment. 



