Parasitic Copepod Tlicrsitina gastcrostei. 421 



Larval Stages. 



The nauplii can readily bo obtained by isolating females 

 with very advanced eggs, but the eggs- -will not hatch when 

 so isolated unless the nauplii are already visible and active 

 within them. The nauplii will live for some time in water 

 not specially aerated, but I have not been able to keep them 

 thus up to the Cyclopid stage. No doubt it would be easy to 

 keep them to maturity with a proper system of aeration. 

 Unfortunately my water-supply does not admit of a satis- 

 factory arrangement. 



The First Nauplius. 



"When first hatched the nauplius is of the usual Oyclopid 

 form and only "11 mm. in length. It is very transparent, but 

 has conspicuous blue pigment round the gut (PI. XII. fig. 2). 



The first antennae are two-jointed, with a single seta at 

 the apex of the first joint and two setae of unequal length 

 at the apex of the second joint. 



The second antenna consists of a stout stem bearing a 

 minute one-jointed endopodite and a large exopodite with 

 a row of six seta3. The stem is constricted, though not seg- 

 mented, into two joints, and has a large masticatory hook at 

 its base. 



The mandible consists of a broad basal segment and two 

 short branches. The endopodite is indistinctly two-jointed, 

 the basal joint bearing a large masticatory lobe armed with 

 two stiff setre. The distal joint bears three setas and a large 

 thick aesthete. The distal end of the body is provided with 

 the usual pair of setas. The anus is apparently imperforate. 



The Second Nauplius. (PI. XII. fig. 3.) 



Six days after hatching the nauplii showed very little 

 change. The length was "16 mm., or a growth of '05 mm. 



The appendages remain as before, except that in the case 

 of the mandible the exopodite is distinctly three-jointed and 

 the endopodite has the appearance of a simple masticatory 

 appendage of the basal joint. It consists of the previous 

 masticatory lobe and a minute knob bearing the large aesthete 

 and three setae. Behind the mandible are seen beneath the 

 skin the rudiments of a fourth pair of appendages. The 

 posterior end of the body has now two pairs of setSB. 



The antenna] gland is present in the form of a long slender 

 tube running back behind the mandible and returning on 



