1910] Alimentary Canal of Psychoda Alternata 287 



the larvae of the blow-fly (Calliphora), but are more often short 

 and inconspicuous. The number of caecae may be two (Cteno- 

 phora), four (Tipula, Simulium, etc.) or many as Miall and 

 Hammond ('00) figure for the larva of the Harlequin fly. Vaney 

 ('02) says that -in Anthomyia there are four caecae, in Chir- 

 onomus many, while in Stratiomyia and Tanypus they may be 

 absent. In Tanypus he finds and figures a group of very large 

 vacuolate cells with ectal diverticula which he claims function 

 as caecae. This group of cells is similarly located, and the cells 

 themselves, except for the ectal diverticula, closely agree with 

 those described above for Psychoda. In Psychoda I am con- 

 vinced that this group of cells is the rudimentary caecal glands. 

 I find it also present in Pericoma. Caecae are said to be entirely 

 absent in the larvae of Lepidoptera, which in this respect would 

 seem to show a relationship between the Psychodidae and the 

 Lepidoptera. There are not wanting a number of other char- 

 acters which indicate such an affinity. 



Behind the caecal gland comes a group of cells very similar 

 to those which secrete the peritrophic membrane (Figs. 14 and 

 15). The cells stain quite deeply, are elongate and extend 

 meso-caudad. They have numerous vacuoles which usually 

 contain large spherical concretions (Fig. 19, con.) The nuclei 

 are large with distinct nucleoli and intensely staining chromatin 

 granules. The posterior extent of this group is marked by a 

 few greatly elongated cells which project into the lumen (Fig. 

 14, ep.) It might be supposed that this group of cells assisted the 

 anterior one in the production of the peritrophic membrane 

 but from repeated examination of my specimens no signs of 

 this have been found. 



Caudad of this region comes a long stretch of fairly uniform 

 cells. They , are very large and cubical or polygonal (Fig. 2, ep.) 

 The ones in front and behind are cubical, while those in the 

 median region are longer than deep. Scattered among the large 

 cells are to be found small slender ones (Fig. 21, ep.) The 

 cells of this region are stained but slightly with iron-haema- 

 toxylin, are finely vacuolate, and possess a narrow but distinct 

 striate border. The nucleus is large and the nucleolus and 

 chromatin are sharply differentiated. These cells are secretory 

 but do not take on the greatly elongated condition found in 

 those farther back during most active discharge of secretion. 



