Introduction to Animal Morphology. 255 



pharyngeal ganglion, sending two lateral, visceral 

 branches, which form two small, lateral oesophageal 

 ganglia, and end in two labial ganglia. From the 

 large ganglia come off laterally nerves to the upper 

 mantle lobe and to the arms. Two cords pass beside 

 the oesophagus, forming a pillar-like pair of gangli- 

 form swellings, sending branches to the ventral mantle 

 lobes. There is no oesophageal ganglion in Lingula, 

 but two lateral ganglia, sending many radial ner\'es 

 in the mantle. Two similar ganglia exist in Discina. 

 Most Brachiopods are hermaphrodite ; a few (The- 

 cidium, &c.) are dioecious. The sexual gland is afour- 

 (rarely two-) lobed yellow mass, either in the body 

 cavity, and partly round the intestine and muscles 

 (Ecardines), or in the space between the mantle lobes. 

 (Testicardines). How impregnation occurs is un- 

 known ; but as they are always in clusters, there 

 would not be much difficulty. The sexes in Thecidium 

 differ in the shape of their shell, and this genus has 

 also a brood-pouch wherein the eggs are retained by 

 fine filaments. The embryology of Brachiopods con- 

 firms strongly their relationship to Vermes. The ova 

 appear first as caudate ciliated bodies, early develop- 

 ing a bilobed mantle, and a velum or ciliated head- 

 lobe, on each side of which are four, hollow, ciliated 

 processes. The free larva has two ear-vesicles on the 

 nerve centres, disappearing in the adult. Eyes also 

 exist as pigment spots, which also disappear. The 

 intestine early develops, and the velum is modified 

 into the arm basis. The fry of Discinse have been 

 found attached to the valves of their parents, and the 

 fossil Stringocephalus has been found with many 

 embr}^o shells within it. Some larvas creep by means 



