158 Pub. Puget Sound Biol. Sta. Vol. 2, No. 44 



be determined by careful reconstructions of sections of the larva, and this 

 was the method of study pursued by the author. 



The digestive system of Salmincola edwardsii is completely developed 

 in the first copepodid larva and consists of a mouth tube, pharynx, oeso- 

 phagus, stomach, intestine and anus. The lips of the mouth tube (Figs. 

 15 and 22, u. 1 and 1.1) are separate at first, and then unite at the base 

 to form an elliptical pharynx (Fig. 16, ph), which runs a short distance 

 to about the place where the second maxillae originate, and there enters 

 the oesophagus. This last named structure (Figs. 11, 17 and 18, oe) is a 

 thin, circular tube, which extends through the rest of the cephalon and 

 enters the spacious stomach (Figs. 11, 19 and 20, st). In Fig. 11, the 

 connection between the oesophagus and stomach is particularly well shown. 

 The stomach is large, cone-like, and most of it lies within the center of 

 the first thoracic segment. In the living state it is filled with spherical 

 yolk globules (Fig. 1, y) which stain intensely black with Heidenhain's 

 haematoxylin. These are the black masses seen in the stomach (st) in 

 Figs. 11, 19 and 20. Toward the posterior region of the first thoracic 

 segment the stomach tapers into a slender intestine (Figs. 11 to 13, and 

 21, i). The intestine is fully developed. It extends thru the middle of 

 the second segment of the thorax and thru the abdomen, terminating in 

 the center of the extreme posterior margin of the third abdominal segment 

 as the anus. This is well shown in Figs. 13 and 14 (an). 



These observations bear out what Claus (1862) has observed concern- 

 ing the digestive system of Achtheres percarum Nordmann, but are not in 

 accord with what Wilson (1911) has found in the larva of Achtheres 

 ambloplitis Kellicott. Wilson says, "Claus has described this first copepo- 

 did stage in Achtheres percarum as possessing a completed digestive system, 

 capable of functioning. But he stands alone in such a statement. Nordmann, 

 Kollar, Vejdovsky and Kellicott all present the larval digestive apparatus 

 at this stage as only partially developed, and thus agree with what was 

 found in the present species." However, it must be pointed out that all 

 the investigators mentioned by Wilson as well as himself, determined the 

 internal anatomy of the first copepodid larvae largely through an examina- 

 tion of the entire animal. As stated above, this method of studying such 

 minute, transparent larvae is rather delusive and inadequate. 



The histological structure of the digestive system is very similar to 

 that of other Crustacea. Interiorly it is lined by a layer of simple columnar 

 epithelium, whose cells contain prominent nusclei. In the stomach these 

 epithelial cells attain a very large size (Figs. 11, 19 and 20, st). Sur- 

 rounding the epithelial layer is a thin outer layer of fibrous connective 

 tissue. Outside of this are the thin mesenteries which suspend the diges- 



