CRUSTACEA. 
303 
segmented body. In obedience to this law the Arguli have 
remarkably strong maxillipeds^ and in this respect have an 
affinity with the Branchiopoda. 
In the manner of carrying the ova Argulus differs from the 
Copepoda, Caligidse, and Ascomyzontidse in wanting both the 
ovisac and outer spermatophore. 
The results of M. ThorelFs researches are embraced under the 
following heads : — 
I. ArgididcB agree generally with the Copepoda, and have certain relations 
of organization in common with the Branchiopoda and Copepoda, 
1. They have receptacnla seminis ; and;, 
2. No parthenogenesis appears to occur. 
II. They differ from the Copepoda in these respects : — 
1. Their extremities have not the characteristic form of the Copepoda. 
2. They have two moveable eyes in front. 
3. The integument of the head is protracted into a divided scutum 
which often covers a great part of the body. 
4. The ova are collected neither in an ovisac nor in the matrix when 
they quit the ovary. 
6. Fecundation does not occur within, but without their bodies. 
6. The larva quits the egg in a much more developed condition than in 
the Copepoda. 
III. But the higher Siphonostoma {Copepoda) agree with them in certain 
respects, which all depend upon the parasitic mode of life, such as 
1. The depressed form of body. 
2. A pair of antennae attached as fixed organs. 
3. The form of the mouth. 
4. The great development of the maxillipeds. 
IV. They differ from the Siphonostoma in these respects : — that, 
1. Only one pair of antennae are fixed organs. 
2. Palpi are wanting ; and, 
3. A spine may be found above the oral siphon. 
4. Two pairs of mandibles (Mundelar) may exist within the siphon. 
5. The first pair of maxillipeds may have the form of suckers. 
V. The Augulidje are related to the Branchiopoda, 
1. In the character of their extremities (appendages). 
2. Structure of the organs of vision. 
3. In general appearance, particularly in the carapace. ' 
4. The want of palpi. 
6. Absence of the ovisac. 
6. Absence of the external spermatophore. 
VI. They approach the Bhyllopoda, 
1. In having the body segmented j and, 
2. In having the eyes not united. 
