636 William Patten 



Seen to be elongated, hyaline fibres, with node-like swellings at 

 various intervals (fig. 111). These bacilli, uuless the position and 

 arrangement had been accurately determined , might be mistaken for 

 the so-called rhabdom of Grenacher, for which in the present instance 

 we have absolutely no equivalent. That no doubt as to the nature of 

 the roda can for a moment be entertained. is shown by their root-like, 

 characteristic ends, and the ease with which , in cross, or longitudinal 

 sections, as well as in macerated preparations', one may demonstrate 

 their continuity with the pigment cells at the outer ends of the ommatidia. 

 Moreover the size of these rods is so great that they form one of the most 

 prominent, as well as easily understood objects in macerated prepara- 

 tions ; they furnish us with a striking proof of the accuracy of previous 

 studies upon this subject, which have failed to reveal the presence of 

 such prominent and simple structures ! This cannot be due to a diffe- 

 rence in the species studied since, in all other Crustacea, as well as in 

 several types of Insect eyes, I have fouud that the bacilli play an 

 equally important part. 



In the Spaces between the diminished inner ends of the ommatidia, 

 is a third group of cells, the boundaries of which cannot be distin- 

 guished, and therefore it is difficult to determine the number belouging 

 to each ommatidium. The nuclei are arranged at various niveaux around 

 the inner ends of the pedieels, seldom far removed from the basal mem- 

 brane (fig. 73 y). The protoplasm of these cells forms a thick sheath 

 around the inner ends of the retiuulae, andcompletelyfillstheintervening 

 Spaces. These cells contain a mass of yellowish, fat-like crystals which, 

 by reflected light, appear perfectly white and opaque, forming, along 

 the inner surface of the ommateum, a narrow and intensely white band, 

 perfectly visible to the naked eye. The crystals, which are very simi- 

 lar to those formed by certain fats , are insoluble in absolute alcohol, 

 clove oil, creosote, Chloroform, or ether. But a very dilute solution 

 of caustic potash dissolves them at once, with the formation of a purple 

 Solution. I thought, at first, that the color carne from dissolved pigment, 

 but soon found that that was not the case, for, after a short time, it was 

 noticed that the formation of the purple solution , instantly produced 

 by the addition of very weak caustic potash , issued only from those 

 parts where the crystals were situated, and further, that in a short time 

 ali the white crystals had disappeared , while the pigment remained 

 unaffected. Moreover the latter was only dissolved by subsequent treat- 

 ment with much stronger caustic potash, then produeing a brown, instead 

 of a purple solution. As already remarked , there is a smaller deposit 



