PEOPLING OF LAND AND SEA 167 



mentary respiratory apparatus. Balanoglossus, a peculiar 

 marine Worm without locomotor bristles, has constructed a 

 respiratory apparatus at its other extremity at the expense of 

 the oesophagus. This consists of a series of symmetrical lateral 

 pockets, communicating both with the oesophagus and with the 

 exterior. This arrangement is found again among Fish such 

 as Bdellostoma and young Lampreys, and is slightly modified 

 in Myxine and the adult Lampreys. The pockets have 

 been replaced by simple slits in all the Sharks and Rays. The 

 separating walls of these slits are now only represented in 

 Sturgeon and Bony Fish by arches covered with a double row 

 of points, arranged like the teeth of a comb. These pockets in 

 Lampreys were also unquestionably preceded by simple slits, 

 since that is the form of the respiratory apparatus in 

 Amphioxus, from which is derived the enormous branchial 

 sac of the Tunicates, constituting a kind of oesophageal abyss. 



In spite of their chitinous envelope, the internal respiratory 

 apparatus of the Arthropods originates from a simple 

 invagination of the integument. This is also the way in 

 which the integumentary glands of these organisms arise, 

 notably the highly important coxal glands, connected with the 

 base of the appendages, which, according to circumstances, 

 become either salivary glands, poison glands, annexes to the 

 proboscis in the Mosquito, the sting in the Bee, or else kidneys, 

 like the green gland of the Crayfish and the analogous gland 

 in Lobsters, Crabs, and their congeners, and which opens 

 at the base of their antennae. This similarity in origin, 

 entailing a certain similarity of organization, has led to the idea 

 that the tegumentary glands, at least in certain cases, 

 can be transformed into respiratory tubes. However this 

 may be, it would seem that four groups of Arthropods, 

 the Onychophora, Arachnida, Myriapoda, and Insecta, have 

 acquired independently an internal respiratory apparatus, 

 constructed in an analogous fashion, in its permanent form 

 at least. 



The species of Pcripatus are peculiar organisms, living under 

 stones, in rotten wood, worm-eaten trees, and in vegetable 

 debris generally. They resemble Caterpillars with membranous 

 feet, and bodies terminating in front in antennae, but without 

 a distinct head. Thus in body type Peripatus also resembles 

 the Annelid Worms, but the body is protected by a chitinous 



