REVIEW OF GENUS ARGULUS — MEEHEAN 469 



The eggs are laid on a hard substratum in single or multiple rows 

 and are arranged end to end or at slight angles to each other. As 

 they are laid they are coated with a gelatinous substance that hardens 

 on contact with the water, forming ridges, lumps, or wrinkles over the 

 surface of each egg and is firmly attached to the eggs and substratum. 



Batches of 30 up to 500 or 600 may be laid, depending upon the 

 species, and vary in size from 0.375 by 0.25 to 0.64 by 0.43 mm. 

 The period of hatching is somewhat variable. Tokioka found that 

 the eggs of A. japonicus hatched in 12 days at 30° C. and in 60 days 

 at 15° C. On the other hand, Wilson noted that A. americanus 

 hatched in 18 days at 65° F. and in 17 days at 72° F., while A. meg- 

 alops required 60 days at the same temperature. Kellicott records a 

 period of 81 days for A. stizostethii at room temperature. According 

 to Wilson (1907), Clark observed A. foliaceus hatching at the end of 

 5 months 8 days, and 7 months 2 days where the eggs were laid in 

 the fall and hatched the following spring. 



Martin's observations on the early embryos throw light on the 

 structure and development of the proboscis. At this time the mandi- 

 bles are incurved with apices directed anteriorly toward the mouth 

 opening and some distance behind it. The basal segment is large and 

 bears a 3-segmented palp with three rami on the terminal segment. 



On later embryos the basal segment has increased in size all out of 

 proportion to the other segments. A rudiment of the lower lip be- 

 comes apparent in a position posterior to the mandibles, while the 

 upper lip occurs anteriorly between the bases. Apparently the distal 

 portions of the basal segments fuse with the upper and lower lips to 

 form walls for the buccal cavity. The cliitinous framework probably 

 forms along the lines of greatest stress, since there is a great deal of 

 individual variation. 



First stage larva. — Larvae of this first stage may be of two kinds — 

 one for the slower-hatching species, which are more fully developed 

 and lack mandibular palps, and another for those that hatch more 

 quickly and are less advanced in development. A. japonicus belongs 

 to the latter group and will be used as an example, since the imma- 

 ture stages have been fully described by T. Tokioka as each molt 

 occurred so that a most logical picture of development can be obtained. 



The length of the hatching animal is 0.7 to 0.9 mm. Its carapace is 

 oval, with short alae and with all the legs, the thorax, and the 

 abdomen left exposed. Only the groove limiting the cephalic area is 

 apparent. The dorsal ribs are unforked, while the joint behind the 

 nauplius eye is lacking. The carapace, ahead of the brown compound 

 eyes, is fringed with chitinous ciliary processes and a few spinules. 

 Along the whole marginal area are many gland cells and some espe- 

 cially conspicuous ones at the base of the first antennae. The stomach 

 has a simple pair of branches, forked only once. 



