424 RICHARD EVANS. 



Hermann's or Flemming's fluid tends to prove that it was of a 

 fatty natui'e. 



(2) The Yolk Bodies. — These bodies are far more numer- 

 ous than the nutritive vacuoles, but the same remarks apply to 

 them as to the vacuoles in regard to their occurrence in differ- 

 ent classes of cells. They are chiefly found in the cells with 

 vesicular nuclei, which, as a rule, contain only one nutritive 

 vacuole, while they contain several yolk bodies, and in many 

 cases they may be described as being full of them. Their 

 average size in the youngest larvae is about 2| fx across, and 

 their shape is either spherical, oval, or plano-convex (figs. 1 — 4). 

 As the larva becomes older, and cell-diff'erentiation progresses, 

 they become smaller in size, and some of them seem to be used 

 up completely, though this is not true of all of them. No 

 larva, even of types C and D, was observed to be absolutely 

 devoid of yolk bodies; on the other hand, they are often very 

 numerous in the fixed stages (figs. 25 and 26), a fact which 

 points to the early fixation and metamorphosis of such in- 

 dividuals. 



They almost invariably stain like the nucleus, but when 

 sections are successfully stained witii carmine, and subsequently 

 with bleu de Lyon, the nuclei take the former, whilst the yolk 

 bodies take the latter (figs. 1, 3 — 6 a, 25, and 26). The outer 

 layer stains more deeply than the central part, which, as a rule, 

 is devoid of any stain, the colourless space being almost circular 

 in shape, and slightly eccentric in position. It happens some- 

 times that this space, instead of being clear, is stained red, 

 while at other times there is a red patch near the border. This 

 space seems to be only a vacuole in certain cases, while in others 

 it is occupied by a substance which stains diff'erently from the 

 bulk of the granule. When sections are stained with Bismarck 

 brown, followed by malachite green, there can be seen in the 

 clear space inside the yolk bodies one or more refringent 

 granules which are devoid of crystalline structure. The 

 granules in question vary considerably in size and shape, 

 having the form of dumb-bells, spheres, or rods, all of which 

 are represented in fig. 4. 



