MORPHOLOGY OF THE COPEPODA. 293 



since it lias been shown, as the indubitable result of numerous 

 researches in the Entomostraca, that they have nothing in 

 the number and conformation of their somites common with 

 the Malacostraca, the notion of the French observers would 

 at once be conti'adicted. On the other hand, when we regard 

 the relation of the parasitic Crustacea with the free Copepods, 

 and their exact correspondence in the mode of segmentation 

 and number of somites, as we have shown to be the case, for 

 instance, in Nicothoe and Cyclops, it will not be in vain to 

 attempt to draw a parallel between the limbs in the two series 

 of Crustacea, and at the same time to explain, morphologi- 

 cally, the differences in structure observable in the various 

 families and genera. 



In all the Copepoda which present a distinct division of the 

 body into the full number of somites, we may distinguish 

 four pairs of oral organs — two mandibles, two maxillae, and 

 four jaw-feet, the latter fulfilling the functions of seizing and 

 masticating the food. The same number is also found to exist 

 in the Saphirmce {vide ' Beitrage zur Kenntniss der Entomo- 

 straken,^ 1 Heft, 1860, Marburg), which may be regarded to 

 a certain extent as stationary parasites {Saphirina salpa, in 

 the branchial cavity of the Salpse), and as constituting in their 

 habits the transition between the free Copepods and the para- 

 sitic Crustacea. These forms, it may be remarked, all possess 

 the characteristic labium in the form of an azygous plate 

 partially overlapping the jaws. 



In Nicothoe we may also count four pairs of oral organs, of 

 which the four maxillary feet (fig. 3 e,f), in conformation 

 and position, precisely correspond with the jaw -feet of the 

 Copepoda. There remain, therefore, the two piercing setse 

 and the palpi, whose homology with the mandibles and 

 maxillse might at first sight be doubted, although one might be 

 justified in explaining the differences in form, as associated with 

 the diversity in the mode of life, on the assumption that they 

 were functional differences. But since we are able in numer- 

 ous parasitic Crustacea to reduce the oral organs not only to 

 the same number, but also to demonstrate a gradual approach 

 in the form of the piercers to the mandibles, and of the palpi 

 to the maxillae, it would seem no longer possible to doubt the 

 correctness of our explanation. The Caliginee and Pandarinoe, 

 whose oral organs, as I have satisfied myself in the case of 

 Caligus, Nogagus, Pandarus, Cecrops, &c., were very well and 

 accurately known, as regards their number and structure, to 

 Burmeister, in the construction of their oral armature have 

 a general resemblance to Nicothoe. Besides the conical pro- 

 boscis, the altered oral hood of the larva, which in the present 



