398 DISCOVERY REPORTS 



digestion by the endoderm cells of proteins, fats, and, to a lesser degree, of some carbohydrates. 

 Whether this is true of the Siphonophora in general has yet to be shown, but there are good reasons 

 for supposing that the two phases of digestion, extra- and intracellular, take place in Physalia. 



The gastrozooids are, of course, the main digestive units. They spread out over the body of a fish, 

 and the surface of the fish dissolves; this can only be the result of extracellular digestion. A partially 

 digested broth then passes into the enteron. In a later stage of digestion, gastrozooids are found with 



5 mm 



Text-fig. 4. Sketch of a gastrozooid showing the main regions, be = buccal region, bs = basal region, c = valve-like con- 

 striction near base, / = fold, m = mouth, v = villus. The endodermal folds and villi are seen through the transparent wall 

 of the zooid. 



1 mm 



Text-fig. 5. Transverse section through a gastrozooid in the buccal region. Inset: an enlarged region, ec = ectoderm, 

 f.en = folded endoderm (secretory cells), gl.ee = ectodermal gland cell, mes = mesogloea, nem = nematocyst. 



their mouths constricted, and their interiors filled with food matter. For reasons given below, intra- 

 cellular digestion can be stated to take place at this stage. We know from Bodansky and Rose (1922) 

 that various enzymes are produced in the gastrozooids, but we are still far from knowing which cells 

 produce which enzymes. In addition to the gastrozooids, we have to consider the palpons, which, 

 from their structure, are clearly concerned in digestion at some stage in the life-cycle, even though they 

 may not play an important role while the gonodendra are still attached to the parent colony. 



The gastrozooid of Physalia consists of two well-defined regions (Text-fig. 4) which will be referred 

 to as the ' buccal ' and ' basal ' regions. The buccal region, consisting of the whole distal half of the 

 zooid, can be spread out as a flat disk in feeding. The basal half is characterized by conspicuous pro- 



