I 



NO. 1783. NORTH AMERICAN LERNJEOPODIDJE^WILSON. 223 



secretion of the cement gland, which forms in the external sacks a 

 thick outer shell membrane. 



4. The first cleavage nucleus divides and with some of the cytoplasm 

 migrates to the surface at a point opposite the wall of the external 

 sack. The migrated materials are there transformed into blastoderm 

 cells by an accumulation of the cytoplasm around nuclear centers, 

 until four or five cells of the same size have been produced. Then, 

 while the migration continues, a segmentation of these cells also begins 

 and the two processes go on simultaneously until the completion of 

 the blastoderm, when the cells composing it secrete a cuticular mem- 

 brane, the blastodermic cuticle. 



5. After the blastoderm has entirely surrounded the yolk the 

 portion of it which is to become the ventral surface of the embryo 

 thickens by a rapid multiplication of cells, and builds up a series of 

 lobes, which are to constitute the future appendages. 



6. The nauplius and metanauplius stages are passed inside the 

 egg, the larva hatching in the first copepodid stage. The first two 

 stages are so completely fused as to be indistinguishable. The 

 nuclear centers of the usual nauplius appendages, of the mouth- 

 parts, and of the first two pairs of swimming legs all appear simul- 

 taneously. The first and second antennre develop quickly into 

 normal nauplius appendages. The mandibles never do but, with 

 the other appendages, are arrested for a time, and then develop into 

 the usual metanauplius form. The nauplius eye is so rudimentary 

 that it can be seen only in serial sections; it has neither pigment nor 

 lenses. 



7. The most interesting nauplius structure is the attachment 

 filament, begun in the nauplius and completed m the metanauplius 

 stage. It is secreted by a large frontal gland which occupies the 

 whole of the anterior dorsal portion of the cephalon. It consists of a 

 long filament, cylindrical and hollow, straight at first then increasing 

 in length and coiling like a rope, the two ends extending forward to 

 the fi-ontal margin. The distal end is shaped like a muslu'oom and 

 is the part attached to the host; the proximal end is peg-shaped and 

 is the point of attachment between the filament and the gland. 



8. The larva emerges in the first copepodid stage a vigorous 

 swimmer, and at once seeks a host and fastens itself somewhere 

 on the gill arches. During attachment or at least before the next 

 molt, the filament is transferred from the frontal margin to the 

 claws at the tips of the second maxillgs. It remains here during life 

 in the female, being gradually shortened down to the length found in 

 the adult. In the male it remains until the union of the sexes, when 

 the claws are withdrawn from it and the male afterwards clings to 

 the body of the female. 



9. The attachment button of the adult, therefore, is the mush- 

 room enlargement at the distal end of the larval filament. It is the 



