LOLIGO PEALII LESUEUR 243 



Respiratory system and mantle cavity. It has been al- 

 ready stated that the body of the squid is surrounded by a 

 mantle which has the shape of a hollow, elongated cone. The 

 mantle is attached to the body along the antero-dorsal surface. 

 The free edge of the mantle, called collar, is kept in position by 

 these equidistant cartilages. Of these the right and left in- 

 fundibular cartilages articulate with the pallial cartilages of the 

 mantle, while the nuchal cartilage articulates with the pen in 

 the upper median line. We have seen besides that inside the 

 funnel is a valve the infundibular valve and on the outside 

 of the funnel are two lateral valves. Water is drawn rhythmically 

 into and forced out of the mantle cavity by the expansion and 

 contraction of the mantle. It enters through the free space 

 between the head and the collar and leaves by way of the funnel, 

 a reversal of the current being prevented by the valves. Sit- 

 uated in the mantle cavity and extending from the heart for- 

 ward to the base of the funnel, are two gills. As the water is 

 drawn into the mantle cavity by the expansion of the mantle, 

 it passes between the so-called pinnae of the gills and leaves the 

 latter by way of the branchial canals. 



Each gill or ctenidium has the shape of a long, trihedral 

 pyramid and consists of a core and the gill proper. The core 

 itself has the shape of a trihedral pyramid and is attached to 

 the mantle by a sheet of integument along the median line of 

 one of its surfaces. The other two surfaces serve as support to 

 the gill proper. The latter may be likened to a plume with 

 triangular barbs or pinnae, which are attached to the core by 

 one edge. The branchial vein runs along the free edge of the 

 gill and corresponds to the stem of the plume. An efferent vessel 

 runs along the free edge of every pinna to the vein. The bran- 

 chial artery runs along the edge of the core, under the vein and 

 parallel to it. It gives off an afferent vessel to each pinna. These 

 vessels run along that edge of the pinna which is attached to 

 the core. The branchial artery is separated from the branchial 

 vein by the branchial canal which runs parallel to them and 



