[197] Van Beneden (No. [506]) in the genera investigated by him finds that the two maxillipeds are really distinct pairs of appendages.
[198] It seems not impossible that the appendage regarded by Claus as the mandibular palp may really represent the maxilla, which would otherwise seem to be absent. This mode of interpretation would bring the appendages of Argulus into a much closer agreement with those of the parasitic Copepoda. It does not seem incompatible with the existence of the stylet-like maxillæ detected by Claus in the adult.
[199] Alepas squalicola is stated by Koren and Danielssen to form an exception to this rule, and to leave the egg with six pairs of appendages.
[200] Willemoes Suhm (No. [530]) states that the mouth is situated at the free end of the upper lip, and that the œsophagus passes through it. From an examination of some specimens of this Nauplius, for which I am indebted to Moseley, I am inclined to think that this is a mistake, and that a groove on the surface of the upper lip has been taken by Suhm for the œsophagus.
[201] The enormous spinous development of the larva of Lepas fascicularis is probably to be explained as a secondary protective adaptation, and has no genetic connection with the somewhat similar spinous armature of the Zoæa.
[202] There is considerable confusion about the shell-gland and antennary gland. In my account Willemoes Suhm has been followed. Claus however regards what I have called the antennary gland as the shell-gland, and states that it does not open into the antennæ till a later period. He does not clearly describe its opening, nor the organ which I have called the shell-gland.
[203] For the characters of Nauplius vide p. [460].
[204] Claus speaks of the various Crustacean phyla as having sprung from a Protophyllopod form, and it might be supposed that he considered that they all diverged from the same form. It is clear however from the context that he regards the Protophyllopod type from which the Malacostraca originated as far more like existing Phyllopods than that from which the Entomostracan groups have sprung. It is not quite easy to get a consistent view of his position on the question, since he states (p. 77) that the Malacostraca and the Copepods diverged from a similar form, which is represented in their respective developments by the Protozoæa and earliest Cyclops stage. Yet if I understand him rightly, he does not consider the Protozoæa stage to be the Protophyllopod stage from which the Malacostraca have diverged, but states on p. 71 that it was not an ancestral form at all.
[205] Claus appears to consider it doubtful whether the Malacostracan gills can be compared with the Phyllopod gill pouches.
[206] Facts for Darwin, p. 49.