306 
BRITISH ENTOMOSTRACA. 
three joints, the terminal one being provided at its ex- 
tremity with several short setae. 
The inferior half of the body of the animal is composed 
of four segments, the first of which is the largest, and has 
on its ventral surface a pair of members exactly similar to 
the last pair described, belonging to the cephalo-thorax. 
The other segments decrease in size as they descend, and 
the last is slightly lobed at the extremity, and furnished 
with several setae. 
The smaller of the two forms of embryo differs in the 
shape as well as the size of the cephalo- thoracic por- 
tion, being ovate, the superior portion broader than the 
inferior, and not expanded laterally. The lower half of 
the body is narrower than the corresponding portion of 
the first form, but consists of the same number of seg- 
ments. 
The eyes and antennae are similar, but the latter organs 
are proportionally larger. 
The foot-jaws are either wanting or so rudimentary as 
not to have been observed, while the last two pairs of 
members are narrower and shorter than those in the first 
form. 
In general conformation we thus find the young of the 
Nicothoe very similar to the young of the Cyclops, and 
we can trace the gradual transformation of the different 
parts of which the animal is composed. The eyes, mouth, 
antennae, and three pairs of foot-jaws already exist, though 
in their progress towards maturity they undergo consider- 
able changes. We find, however, only two pairs of 
swimming-feet, while in the adult there are five. The 
two upper pairs become smaller, but assume a branched 
form, and the three others are added during the animal’s 
progress towards maturity. The whole body consists, in 
the young, of five segments, in the adult of ten ; five rings 
are thus added during its growth, before it reaches the 
full-grown state. 
In general form, the Ergasilidse appear to connect the 
Cyclopidae with the Lerneadae ; but in habits and mode 
