58 BULLETIN OF THE 



If this course of development really takes place, the various structures 

 in the eye of an adult Argulus can be easily homologized with those 

 in Amphipods. Tluis the corneal hypodermis and corneal cuticula of 

 Ainphipods would probably be represeuted by the hypodermis and cu- 

 ticula dorsal to the eye in Argulus (Fig. 11). The basement mem- 

 brane of this hypodermis would correspond to the corneal component 

 of the corneo-conal membrane of Ainphipods, and the conal constituent 

 Avould be represented by what is called the preconal membrane in Argu- 

 lus (Fig. 11, mb. pr'con.). Proxinially, the preconal membrane becomes 

 continuous with the sheath of the optic nerve (Fig. 11, mb. n. opt.), 

 the equivalent of the capsular membrane of Amphipods. The basement 

 membrane of the retina in Argulus, as in Amphipods, is tlie membrane 

 pierced by the fibres of the optic nerve (Fig. 11, mb. ba.). 



Grobben ('79, p. 258) has suggested that possibly the eye in Argulus 

 is of the same type of structure as in Phyllopods, but I do not share 

 in this opinion for the following reasons. In Estheria, the delicate 

 cuticula which covers the optic stalk is morphologically a portion of 

 the outer surface of the body, and, as I hope to show subsequently, is 

 subtended by a true corneal hypodermis. There is no corneal h^'po- 

 dermis beneath the preconal membrane of Argulus. Moreover, there 

 is nothing in the eye of Argulus to correspond to the optic pocket of 

 the Estheridpe, or to the optic sac of the Cladocera, except the circum- 

 retinal blood space, and it seems to me very improbable that this space 

 was once a cavity in communication with the exterior, and afterwards 

 became converted into a blood space. I therefore believe that the 

 plan of the eye in Argulus is not similar to that in the Phyllopods, 

 but rather tliat it represents a modificdtion of the type presented by 

 the Amphipods. The satisfactory determination of this question can 

 be settled, however, only b}^ embryological evidence. 



Eucopepoda. — In adult specimens of those true Copepods which 

 possess rudiments of tlie lateral eyes, — the Pontellidre and Corycaeidse, 

 — the retina is apparently separated from the hypodermis. In the 

 Corycseidse it usually lies at some considerable distance from the hypo- 

 dermis, and in Pontella the two struclures, although near one another, 

 are nevertheless not continuous. 



The development of the lateral eyes in the Corycteidic and Pontel- 

 lidfe has not been studied, and consequently it cannot be stated witli 

 certainty whether the retinas in these Crustaceans originate from the 

 hypodermis or not. In the metanauplius larva of Cetochilus, a Copepod 

 which as an adult has no lateral eyes, Grobben ('80, p. 262) has de- 



