NOTES. 3879 
affinity of Brachiopods to the Worms. Davidson, however, retains them in 
their old position, as a class independent of, but related to, the Mollusea, 
By many, the Tunicates are joined to the Brachiopods ; by others, they are 
called Worms in disguise. 
159 There are some exceptions: the Oyster is unequivalved, and the Lveten 
equilateral. 
151 The chief impressions left on the shell are those made by the muscles 
—the dark spots called ‘‘eyes”’ by oyster-men ; the pallial line made by the 
margin of the mantle; and the bend in the pallial line, called pallial sinus, 
which exists in those shells having retractile siphons, as the Clam. 
152 The Pearl Oyster has a small, anterior muscle in the umbo, and the 
Spondylus has teeth. 
153 The muscular impressions in Tridacne are blended into one. It is con- 
jectured that this is the case in the Oyster. 
154 The Clam is the highest of Lamellibranchs, and the Oyster one of the 
lowest. The Venus arenaria, or ‘Soft Clam,’ has its mouth always open a 
little ; while V. mercenaria, or ‘‘ Hard Clam,”’ keeps its mouth closed. 
155 The Slug has no shell to speak of, and the Chiton is covered with eight 
pieces. It may be remembered, as a rule, that all uniyalve shells in and 
around the United States are Gasteropods, and that all bivalves in our 
rivers and lakes, and along our sea-coasts (save a few Brachiopods), are 
Lamellibranchs. 
186 That is, if viewed with the aperture facing the observer. Shells twist- 
ed in the opposite direction are called ‘‘ left-handed.” 
187 Such as Dentaliwm, which may be a Pteropod, and the swimming Nu- 
cleobranch, as Carinaria. 
18 Instead of a strong breathing tube with a valve, answering for a force- 
pump and propeller, as in the Cuttle-fish, it has only an open gutter made 
by a fold in the mantle, like the siphons of the Gasteropods. The back 
chambers are filled with nitrogen gas. 
189 The common Poulpe has two thousand suckers, each a wonderful little 
air-pump, under the control of the animal’s will. 
160 Hence the theory of Spencer, favored by Wallace and Clark, that Artic- 
ulates are compound animals, each segment representing an individual. The 
dorsal tube is probably homologous with the right ventricle. 
161 The order is one of relation rather than of rank. The classes can not 
be arranged serially. The Myriapods have a worm-like multiplication of 
parts, degrading them, and their nervous system is simpler than that of Cat- 
erpillars ; yet their heads show a close relationship to Insects. The Arach- 
nids include some lower forms than Myriapods; on the other hand, for their 
wonderful instincts, Owen places them above the Insects. They are closely 
allied to Crustaceans, and stand more nearly between Crustaceans and In- 
sects than between Myriapods and Insects. The higher Articulates begin 
life as worm-like embryos. None of the air-breathers have two pairs of 
antenn, while the aquatic classes may have.—Articulates with jointed ap- 
pendages articulated to the body are called Arthropoda. 
62 The joints of the Tape-worm are not true segments, only successive 
growths containing ova. The true animal is the so-called ‘head.’ The 
