8 



ARKIV FÖR ZOOLOGI. BAND 7. N:0 30. 



tioned. There are no glands in the stomach. A section 

 through a non-inflated specimen shows, as is illustrated in 

 the photographical figur e 1 on Pl. I, a great number of large 

 folds along the ventral wall of the air-sac. But all these 

 folds are smoothed out when the sac is inflated, as I ha ve 

 found from a section made through such a specimen. The 

 epithelium of the air-sac consists of small cylindrical cells. In 

 the connective tissue two layers of non-striped muscle-fibres 

 will be found, one interiör and transverse, one exteriör and 

 longitudinal. The muscular layers are very thin, most deve- 

 loped on the ventral side. The connective tissue is remar- 

 kably well developed. It forms a continuum with a subcu- 



Fig. 5. Spheroides testudineus L. ar. s. air-sac; c. t. stratum of connective 

 tissue; du duodenum; Im longitudinal muscle; Im' anterior head of a part of 

 the longitudinal muscular layer that attachés to the ligament between the ven- 

 tral ends of the pectoral archs; oes oesophagus; p. c. pericardial cavity; per pe- 

 ritoneum; sk skin; sph sphincter muscle in the fold between the stomach 

 and the air-sac; st stomach; irTn transverse muscular laver. 



taneous layer on the ventral side of the whole body. (Pl. I, 

 fig. 1.) A more detailed description of this peculiar stratum 

 will be given in the section on the integument. Exteriorly 

 to this stratum there is a layer of longitudinal, and exteriorly 

 to this a layer of transverse muscles, which are of great im- 

 portance for the emptying of the air-sac. For this function 

 I refer to the second chapter in this paper; the homology of 

 these muscles will form a part of the subject of a separate 

 section in this series of studies on the Plectognaths. There 

 are no glands in the wall of the air-sac. The duodenum is 

 sharply marked off by a pyloric sphincter muscle. 



