The Anatomy of Chlamydoselachus 419 



position it is probably somewhat coiled about these portions of the digestive tube, but 

 in Text-figure 72 it is shown displaced to the left. The color of the spleen, in my pre- 

 served specimens, is a very dark bluish-gray. In my specimen No. I the spleen measures 

 80 X 10 X 3 mm. ; in No. II, 60 x 10 x 4 mm. ; in No. Ill the spleen could not be found and 

 had evidently been torn away. 



From specimen No. I, a transverse segment of the spleen was removed for sectioning. 

 Under the microscope the sections were found to consist mainly of lymphoid tissue con- 

 taining an abundance of leucocytes and many extra vascular erythrocytes; small arteries 

 and veins were distinguishable. In its finer structure the spleen proper is very much 

 Uke the accessory spleen already described in association with the ventral pancreas. 



Hawkes (1907) states that the spleen of Chlamydoselachus is divided into two parts 

 which are separated by a space of 40 mm. The additional "lobe" (which is apparently 

 comparable to what I have called the accessory spleen) is situated to the right of the 

 stomach and somewhat dorsally. It is an ovoid body, 30 mm. long and nearly 20 mm. 

 broad in its widest part, and is situated between the stomach and a fold of mesentery 

 which supports the latter. The other part or spleen proper lies in the usual place at the 

 angle of the stomach. The spleen proper, when examined by a low-power lens, presents 

 the usual appearance; but the additional ''lobe" is much more compact. Hawkes does 

 not mention a pancreas in association with the secondary spleen. 



In Chlamydoselachus, Deinega (1925, Fig. 1) shows, indistinctly, an organ labeled 

 spleen, which appears to be on the right side of the body since it is crossed by the common 

 bile duct on its way from the right lobe of the liver to the intestine. In Heptanchus, the 

 spleen (Daniel, 1934, Figs. 119 and 120) is much more extensive, and is broken up into 

 several different parts or "lobes." 



In concluding this section I note that the digestive system of Chlamydoselachus 

 presents the following features of especial interest: (1) The great variability in the 

 region of transition from stomach to intestine; (2) the differentiation of the coils of the 

 spiral valve into two series, with apices facing in different directions; (3) the presence 

 of an axial strand in the middle portion of the valvular intestine, along with an axial 

 tube in both anterior and posterior portions; (4) the great length of the lobes of the 

 liver, in adaptation to the form of the body; (5) variations in the position of the opening 

 of the common bile duct into the intestine ; and (6) the presence of an accessory spleen 

 associated with the ventral pancreas. In some specimens, there is (7) a persistent thyro- 

 glossal duct which is lined with stratified squamous epithelium and which possesses 

 rudimentary denticles. 



THE RESPIRATORY ORGANS 



In Chlamydoselachus, as in other fishes, the gill-filaments and their lamellae are the 

 primary organs of respiration. Accessory structures such as the branchial skeleton and 

 musculature, the oral breathing valve and the valvular gill-folds or gill-flaps, are concerned 



