161] LIFE HISTORY OF GORDIUS AND PARAGORDIUS—MA Y 41 



elongated and in that respect resemble muscle cells (Fig. 102) . These cells 

 are themselves covered by the layer of mesenchyme cells that later lines 

 the muscles. Ultimately, however, there is no difference between the 

 prenchyma cells that originally covered the nerve cord and those that later 

 migrated over them, the one passing gradually into the other (Fig. 106). 



At times the intestine becomes separated from the underlying layer 

 and remains attached to it by a longitudinal sheet of cells of single thick- 

 ness, the ventral mesentery. The intestine adheres to a broadened surface 

 of the terminal cell, but its outer membrane is in no way continuous with 

 the covering of that cell. The structures by which the egg masses appear 

 to be suspended in the older females are not mesenteries but the remains 

 of the ovaries and will be discussed in the next section. 



Reproductive organs. In the early stages one can find no difference 

 between males and females. The first difference appears in the character 

 of the diverticula formed at the posterior end of the intestine. In the female 

 three diverticula are formed (Fig. 109), one for the seminal receptacle and 

 two for the oviducts, while in the male only two appear for the sperm 

 ducts (Fig. 29). These diverticula have made their appearance before the 

 28 day stage (Figs. 64, 65). Somewhat later the ovaries become differ- 

 entiated from the testes by the formation of buds along the ventral sides 

 (Figs. 76, 84, 86). These buds are not always opposite in the two ovaries 

 nor are they of uniform size (Fig. 62) . 



Each ovary at first is enclosed by a definite, heavy membrane, but 

 later the membrane becomes thin at the buds and the eggs pass into the 

 body cavity soon after they have begun the growth period (Figs. 76, 84, 86). 

 The eggs, however do not lie loose in the body cavity, but continue to be 

 enclosed in thinner membranes of the ovary. By the time the first eggs 

 have reached their full size nearly all of the germ cells have left the ovarian 

 tubes and have in masses, strands, or sheets become distributed among 

 the developed oocytes which tend to form layers around them. As the 

 increase in the diameter of the body continues, the ovarian tubes become 

 broadened dorso-ventrally, and by the discharge of the germ cells they 

 become flattened, so that they take the form of broad, thin sheets suspend- 

 ed from the dorsal muscles (Fig. 79) . In later stages they remain as double 

 membranes still helping to support the masses of eggs in the body cavity. 

 The extensions of the membranes at the buds have become thrown into 

 many folds and have been thickened in places to help in the support of 

 the ovarian mass. At the time of the discharge of the eggs the membranes 

 become ruptured and the heavy parts remain attached to the dorsal muscles 

 (Fig. 46). 



The growth period in the oocytes begins somewhat before the homo- 

 geneous layer is formed under the larval cuticula and continues until the 

 formation of the adult cuticula is well under way (Figs. 76, 86, 77). It does 



