. Text-book of embryology. Embryology. 206 INVERTEBEATA has been worked out by H. Wilson (1911). The adult lives on the gills of the rock-bass, AmUopUtes rupestris : it is a sac-like organism fixed by two â¢conjoined arms to the host; it shows no trace of Copepod structure except the long egg-tubes, which the female bears protruding from the end of her body. If we were to classify by adult structure alone, no one would dream of regarding Ac- theres as a Copepod; hut yet every zoologist is fully convinced that Adheres is a modified Copepodâthat is to say, that it is descended from an anc
. Text-book of embryology. Embryology. 206 INVERTEBEATA has been worked out by H. Wilson (1911). The adult lives on the gills of the rock-bass, AmUopUtes rupestris : it is a sac-like organism fixed by two â¢conjoined arms to the host; it shows no trace of Copepod structure except the long egg-tubes, which the female bears protruding from the end of her body. If we were to classify by adult structure alone, no one would dream of regarding Ac- theres as a Copepod; hut yet every zoologist is fully convinced that Adheres is a modified Copepodâthat is to say, that it is descended from an ancestor which was like Cyclops or Calanus or some other typical Copepod genus. Now the Nauplius and Meta- nauplius stages are completed inside the egg membrane, and the young animal hatches out as what is termed a Gopepodidâ namely, in a form which every one would recognize at a glance as showing the typical structure of a Copepod, that is, of the ancestor. When, however, we look closely at this Gopepodid larva we find that it differs from an ordinary Copepod in the following points:â(1) There are but two free segments in the thorax each carrying a pair of forked swimming appen- dages, whereas five such segments on the normal Copepod carry four pairs of forked swimming appendages and one rudimentary pair; (2) the exo- podites and endopodites of these legs are not divided into joints, while the corresponding members in an ordinary Copepod are many-jointed; (3) the first antennae are short, stumpy, and lew-jointed, as contrasted with those in an ordinary Copepod, where they are normally long and composed of many joints ; (4) the second antennae in the Gopepodid are likewise exceed- ingly short, and although forked each branch is unjointed and the inner one terminates in a hook, whereas hook - like termination is not found; Fig. 152.âDorsal and lateral views of just- fixed female of Adheres amUopUtis. (After Wilson.) A, dorsal view. B, lateral view. Letters as in lireceding ti
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