Contributions to the Anat-^imy and Histology of Thalassenaa neptuni Gaertnor. 547 



pharynx by the presence of an outer layer of longitudinal muscles 

 and the more numerous gland cells. The musculature is never strongly 

 developed, generally one or two strata of fibres in each layer (Fig. 15 

 cm, l.m). As we follow the oesophagus backwards in a series of 

 sections its walls become more and more glandular. The glands 

 (Fig. 15 gl^ gl') resemble those of the crop (see below), but are never 

 so numerous nor so strongly developed. The transition to the gizzard 

 is sudden and well defined. 



The gizzard (Figs. 11 and 12 gf, Fig. 16) is always ventral in 

 position lying on the left side somewhat behind the level of the seg- 

 mental organs; it averages in well grown individuals about 5 mm in 

 length but may occassionally be longer. It is distinguishable to the 

 naked eye by its glistening muscular walls. The dorsal mesentery is 

 absent on the gizzard. 



On examining sections the musculature is found to be very much 

 thickened and the epithelium correspondingly reduced (Fig. 16). The 

 chief thickening occurs in the circular musculature (cm), but the 

 longitudinal layer {l.m) is also strongly developed. The individual 

 fibres themselves are also thicker than on the oesophagus. In some 

 examples the musculature exceeded the epithelium in thickness. Natur- 

 ally the relative dimensions are quite arbitrary, depending upon the 

 degree of contraction of the various parts. The epithelium is, in com- 

 parison to that of the oesophagus, very much simplified, the gland 

 cells are not represented, the columnar cells, resembling the "Faden- 

 zellen" of the epidermis, are almost exclusively present, although I have 

 seen also "basal cells"*). The cuticle of the gizzard is apparently 

 thicker than that of the remaining parts of the digestive system. 

 One can see very well in this region the connective tissue basis to 

 which the epithelium is attached; it is in fact the fibrillar matrix 

 which we have seen in the skin and proboscis surrounding the muscle 

 fibres, and presents here the same relations. These two divisions, 

 oesophagus and gizzard, I regard as homologous to the oesophagus 

 of Echiurus and Bonellia, but, as I cannot draw a hard and fast line 

 between pharynx and oesophagus, I have perhaps given the oesophagus 

 a slightly longer forward extension than Spengel or Rietsch. Horst's 

 figure of Hamingia shows the oesophagus divided into an anterior 

 thin-walled and a posterior thick-walled region, which suggests the same 

 condition as in Thalassema neptuni (8, fig. 3 oe). 



1) 8PKNÜEL (17) applies this term to clear ovoid cells lying between 

 the basal parts of the epithelial cells. 



