ON THE DEVELOPMENT OF PARASITIC COPEPODS. 57 



The only crustacean whose cell lineage has hitherto been 

 carried beyond the 16 cell stage is Lepas, as described by Biglow 

 ('02). Pedaschenko pointed out the resemblance between the 

 segmentations of Lepas and parasitic copepods and I believe this 

 resemblance is fundamental. The endoblast arises one generation 

 earlier in Lepas \ha.n in parasitic copepods but this may be due to 

 larger amount of yolk in the latter, which causes a retardation in 

 the segregation of organ-forming substances, and of gastrulation. 



Canu ('92) published a paper which I have not seen, which 

 included embryology of copepods. Further consideration of the 

 literature may be found in the text. 



I. CLEAVAGE OF THE EGG. 



i . Licinargns muricatus Kroyer. 



A. First Cleavage. --At the earliest stage I have (Fig. 19) 

 the male and female pronuclei lie side by side at the center of 

 the egg and at the equator of the spindle. At this stage the egg 

 throws out a number of yolk spherules into the space between the 

 egg and the chorion, but the exact nature of this process seems 

 obscure. Each pronucleus contains a nucleolus, and the chro- 

 matin is being aggregated into chromosomes. The pronuclei are 

 of the same size and apparently similar in every respect. There 

 is a deeply staining centriole at each pole of the spindle, sur_ 

 rounded by a layer of hyaloplasm that is drawn out into astral 

 rays connected with the surface of the egg, and mantle fibers 

 connected with the pronuclei. The astral rays of one pole are 

 thicker (stronger) than those of the other. Where the mantle 

 fibers come in contact with the nuclear membrane, the latter is 

 pushed in (and partially dissolved?) and finally becomes dis- 

 solved, and the mantle fibers become attached to the chro- 

 mosomes. The spindle thus formed is elongated. The astral 

 rays of one pole shorten more rapidly than those of the other, 

 drawing this pole nearer one edge of the egg than the other. 

 The hyaloplasm is drawn from between the yolk globules and 

 the astral rays increase in thickness. Not only is the hyaloplasm 

 drawn into the astral rays, but small lumps of hyaloplasm adhere 

 to their surfaces and move toward the centrosomes. Thus the 



