173] LIFE HISTORY OF GORDIUS AND PARAGORDIUS—MA Y 53 



from mesenchyme and in the later stages have heavy walls similar to those 

 of the parenchyma. 



Parenchyma and mesenteries. The parenchyma arises as in the preceding 

 species, but fills the body cavity more completely in the early stages. It 

 not only forms the lining for the muscles and surrounds the testes in the 

 males, but it also surrounds the ovaries in the females. As the ventral 

 buds in the ovaries appear and the eggs fill the body cavity, the inner walls 

 of the ovaries become extended around the intestine to the sides of the 

 nerve cord, and in that way the two mesenteries are formed (Fig. 158). 

 The outer walls of the ovaries are turned back upon themselves at the 

 points where the buds arise, and thus double lamellae are established reach- 

 ing from those points to the muscles on the dorsal side of the body. There 

 the layer of each lamella that lies next to the original ovarian tube is con- 

 tinuous over that tube with its inner wall, while the outer layer of the 

 lamella is continuous with the outer covering of the ovarian bud, passing 

 close to the lining of the muscles, around to the ventral side to join the 

 ventral edge of the mesentery, or inner wall of the bud. As development 

 proceeds, the germ cells leave the primary ovarian tubes, just as they do 

 in Gordius robustus, and the outer walls of these tubes appear as parts of 

 the mesenteries. As a result the mesenteries in later stages appear to be 

 composed of three layers of cells in the dorsal part of the body, but of a 

 single layer in the ventral part (Fig. 159). Even in the males the paren- 

 chyma forms about the gonads more definite layers than were found in 

 Gordius robustus (Fig. 174). 



During the formation of the adult cuticula heavy walls appear about 

 the parenchyma cells, in many cases much heavier than in the previous 

 species (Fig. 164). The cells are normally somewhat elongated, poly- 

 hedral or barrel-shaped (Figs. 3, 164), but may in other cases have the 

 irregular polyhedral form found in Gordius robustus. The cells in this 

 species remain more intact and more completely fill the spaces. 



In the anterior end, behind the dorsal group of ganglion cells, the mesen- 

 chyme cells become crowded together very closely and form a capsule 

 which encloses the ganglion cells on all sides except that covered by the 

 flattened anterior surface (Figs. 153-4). This capsule is formed just before 

 the heavy cell walls appear. Its adult structure has been adequately 

 described by Montgomery. 



Reproductive organs. The germ cells a.rise 2iS in Gordius robustus, dind in 

 early stages can not be distinguished from mesenchyme cells in other parts 

 of the body (Fig. 136). In the middle of the body the gonads assume a 

 definite shape before they become surrounded by mesenchyme cells, which 

 at that time have become easily distinguishable (Figs. 147, 156, 157). After 

 that the mesenchyme proliferates very rapidly and completely envelopes the 

 gonads with definite layers. The gonads of the two sexes can not be dis- 

 tinguished in the early stages. 



