ON THE DEVELOPMENT OF PARASITIC COPEPODS. 63 



formed. Fischer ('99) varied this experiment in a number of 

 ways, and one of his experiments . modified slightly, might be 

 tried by every one interested in the subject without much 

 trouble : Spread a layer of egg albumin (which consists chiefly 

 of albumin and a little globulin) on a slide and through a capil- 

 lary tube introduce a small drop of a fixing solution into the 

 albumin, observing the changes that take place under the micro- 

 scope. The albumin immediately around the drop is coagulated 

 into a membrane through which the fixing solution diffuses and 

 from which radiations begin to form, giving the whole structure 

 the appearance of an aster with the drop of fixing solution and 

 the membrane around it as the centrosome. If the rays form, 

 as they seem to, by mutual attraction of the drops or particles 

 in the fluid, such rays or rows of drops would exert a pulling 

 force, and if their ends were released should shorten by synaeresis 

 into a spherical mass. This may be the nature of the fibers of the 

 karyokinetic figures in the cleavage of these copepods but does 

 not explain the direction of movement of the asters. 



III. MESOBLAST. 



i. Nauplius Mesoblast (Pandarus sinuatns, PI. IV. and V.). 



When the cap of the protoplasmic cells has covered about one 

 third of the yolk some of the marginal cells (lip of the blasto- 

 pore) become differentiated as mesoblast. Of these one or more 

 on the right and left edge will give rise to mesoderm of the first 

 and second antennae, and one near the middle of the ventral side 

 and distinguished by its large nucleus (Fig. 37) will give rise to 

 the sex or germ cells. 



A. The Gcnn Cells. This primary germ cell is turned under 

 the rim of the blastopore (Fig. 38) and divides by a sagittal fur- 

 row into two (Figs. 39-40), which lie about the center of the 

 ventral side just under the ectoderm. About the time of the 

 closure of the blastopore these two divide by transverse furrows 

 into four (Fig. 41). This group of four cells rotates until one 

 cell is anterior, two lateral and one posterior. (In Fig. 42 the 

 rotation is not quite completed.) But there is considerable vari- 

 ation in the amount of rotation (Figs. 41-48). The four germ 



