ON THE DEVELOPMENT OF PARASITIC COPEPODS. 45 



have distinguished only one polar body in later stages, which on 

 account of its size I regard as the first polar body or both polar 

 bodies fused (Fig. 49, P\ It may be that the second polar body 

 remains in the egg as in Cyclops and is not easily distinguishable, 

 or more probably it is extruded immediately under the first polar 

 body and the two being pressed together and becoming very flat, 

 appear as one. The chromosomes in the first polar body do not 

 swell and fuse to form a nucleus. 



I have made no observations on the entrance of the sperm. 

 Vide under Polarity of the Egg. 



B. L&margus muricatus (Fig. 18). - - Maturation in this species 

 is very similar to the process in Pandarns. The disintegration 

 of the single large nucleolus shows many stages which appear 

 to be peculiar to this species. A number of vacuoles (globules 

 of achromatic fluid) appear in it, and these sometimes fuse into 

 a single mass. The chromatic substance does not remain as a 

 continuous peripheral layer but rounds up into four or more 

 masses whose inner surfaces are hemispherical and outer surfaces 

 form portions of the general surface of the nucleolus. In some 

 cases there are two fluids (one colorless and the other staining 

 very faintly) formed within the nucleolus. The colorless fluid 

 forms a large sphere in the center and the faintly staining fluid 

 occupies the periphery and contains spheres of the original chro- 

 matic substance of the nucleolus. The chromosomes do not go 

 as far in metamorphosis as in Pandarus. In the equatorial plate 

 the chromosomes appear as short double rods (Fig. 18), and 

 if we regard the spireme formed of chromosomes joined end to 

 end and cut into half the usual number of pieces the first matu- 

 ration division is equational and the second reducing. On the 

 other hand if chromosomes pair in the synapsis stage and lie 

 parallel to form double rods, the first division is reducing and 

 the second equational. The chromosomes cannot be distin- 

 guished all through the resting period, and whereas I am inclined 

 toward the view that each rod of the double rod represents a 

 chromosome, I have not sufficient direct evidence to be sure that 

 this is the case. 



C. The Dichelestid. - -Toward the close of the growth period the 

 nucleus undergoes an enormous change. The nucleoli become 



