CHIRONOMUS PRASINUS. 71 



what in character in different parts, but are all of considerable 

 size, nucleated, and generally polygonal from mutual pressure. 

 In the anterior portion of the stomach some of these cells are 

 lodged in short, dome-shaped, csecal projections of the external 

 membrane; which occur in the midst of square areas, marked by the 

 crossed, longitudinal, and transverse fibres of the muscular coat — 

 see Figs. 5, 26, and 27 — and these frequently present a regularly 

 granulated aspect, and are then more hyaline and colourless than 

 elsewhere ; but in every part of the stomach, and in the proventri- 

 cular caeca the cells are frequently invested with a thick secreted 

 envelope, through which pass a multitude of radiating pores (pore 

 canals ; see Fig. 20), by which the contents of the cells are 

 retained in communication with the surrounding fluids, the pro- 

 cesses of growth and secretion are enabled to be carried on. 



Sometimes the secreted envelope retains its integrity while a 

 process of cell multiplication goes on within it, the envelope 

 increasing in size with the multiplication of its contained cells; thus, 

 larger aggregations of cells are formed, surrounded by a common 

 envelope, as shown in Fig. 20. I will here take the opportunity 

 of quoting one or two extracts from Kblliker * on the subject of 

 these cells and their envelopes : — " My observations on the 

 cuticular structures have shown that secondary depositions from 

 the cells, analagous to the cellulose membrane of vegetable cells 

 are to be found in a great many places, and are often characterised 

 by a very particular structure, especially by the existence of a 

 large number of extremely fine pores, pervading them in the 

 direction of their thickness." And again, KoUiker states that 

 such cells are found on the villi of the human intestine ; for in 

 reference to this subject, he says : — " I have recently shown that 

 the membranes of these cells " (the epithelial cells of the vilH) 

 " are thickened and very finely striated at their free surface, and 

 that these thickened parts represent as it were, in their totality, a 



reaction, and concludes that it is by the aid of these alone, that in insects the 

 digestive process is carried on. He endeavours to show, on chemical grounds, 

 that this is far from being so impossible as it might at first sight be supposed 

 to be. He thinks that in insects there is nothing corresponding to the stomach 

 of vertebrates, and that, what is usually, and as above, called the stomach, is 

 more akin to the vertebrate intestine. 



* Kolliker's Manual of Human Microscopic Anatomy, pp. 26 and 328. 



