HETERONEREJS STAGE OF NEREIS KOI51EXSIS McINTOSH. 22/ 



lost is indicated further by the fact that by gently pressing on 

 the surface of the body wall, eggs may be moved from one 

 somite to another or through several somites. 



Dissection and the study of transverse sections confirm these 

 conclusions. By the loss of the transverse septre the whole 

 interior of the body has been transformed into a continuous thin- 

 walled sac, filled with ova from one end to the other. No trace 

 of ovaries could be found, and, owing to the poor preservation 

 of the material nothing definite can be said concerning the histol- 

 ogy of the internal organs, but there is every indication of a con- 

 siderable amount of degeneration. While the pharynx retains 



</{ ' ^ I -^-^ NOS OsE!S5s ^ fi "5) 



x^-JW-iJ' i, ... "TO 5 . :> _V,- u -i ) - 



Fie. i. Section through anterior region of body of female. 

 blood vessel ; ////, intestine ; >icr, ventral nerve cord. 



X 2 4- 



its normal condition the intestine appears on gross dissection as 

 a mere thread, and anteriorly, the thin transparent body wall, 

 lacking most of its usual muscle layers, is very noticeable. 



Fig. i is from a transverse section through the anterior end 

 of the body, thus through the " unmodified " region. The body 

 wall, with the magnification employed, appears as a mere line, 

 with the thin layer of longitudinal muscle fibers showing as rows 

 of dots just inside it. These muscle fibers are more or less 

 broken away from the rest of the wall, but I cannot tell how 

 much of this is due to actual degeneration, and how much to 

 defective preservation and faulty microtome technique. A small 



