490 THE VOYAGE OF H.M.S. CHALLENGER. 



opposite side. In the brain tliere exists a powerful commissural system, from whicli 

 jiortions reach laterally into the powerful optic-ganglia. 

 IG. The ganglion-cell-lavers are thickenings of the superficial layer. Inner ganglionic nuclei do 

 not exist. The small-celled ganglion formation of the cap-shaped hinder lobe answers to the 

 fungus-like structure on the brain of the higher Crustacea and insects. 



1 7. Tlie optic-fibres of the lateral eye and of the frontal eye run in planes that cross at nearly a 

 right angle. 



18. Each eye is surrounded by a firm sheath, the continuation of the outer nerve-sheath of the 

 brain, which also wraps itself over the front surface^ and before each complex of two 

 crystal cone-cells between the rounded vesicles of theii- nuclei contains two flat oval nuclei. 



19. The cuticular cornea is not derived from the crystal cone -cells, but from a special hypodermis- 



layer separated from those cells by the eye-sheath, and is renewed at the time of exuviation. 



20. The eye continuously increases in extent with the growth of the bodj', by the formation of 



new peripheral elements. 



21. The objection to the possibility of mosaic vision based on the form of the crystal cone is 



thoroughly untenable. [At p. 72, Glaus expresses his agreement with Grenacher's oisinion, 

 that the HyperidiB are not dim-sighted.] 



22. At the ovary there is a special germinal layer. The geniculate terminal section of the oviduct 

 ends with a sack-like expansion in a seminal pocket. 



Of parasites, Claus found in the crop of Plironima and PhronimeUa almost constantly a little 

 oval Gregarine, free or encysted ; more rarely, in the body-cavity of Phronima, embryos of 

 Ecldnorliynehi, and sometimes in the brain a young Nematode, spirally rolled. 



To judge by the short list of literature on page 81, Claus was unacquainted with the papers on 

 the pelagic Amphipoda by Dr. T. H. Streets, which are dated 1877 and 1878. 



1879. Claus, C. 



Die Gattungen unci Arten der Platyscelicleu in systematisclier Ubersiclit. Wien, 

 1879. (Separat-Abdruck aus den Arbeiten des Zoolog. Instituts zu Wien, Tom. II., 

 Heft 2.) 



This work, which has been since its publication the leading authority on the group with which 

 it deals, is practically embodied, though with a few modifications, in the larger and finely 

 illustrated work by the same author published this year (1887). 



It is noticed that in external form the Platyscelidae show an astonishing number of gradations 

 from the egg-like Typhidse to the rod-like Oxycephalidre. The common features are to be 

 found in the structure of the antennse in the male and of the fifth and sixth thoracal legs 

 (third and fourth perfeopods) in both sexes. Five families are established, in two divisions, 

 division A. containing the Typhidse and Scelidaj, division B. the Pronoidae, Lycaeidte and 

 Oxycephalida?. In 1887 the Lycaeidje form a sejaarate division. 



The Typhidre contain five genera: — 1. Eufi/phis, taking the place of Tijplns, Eisso, preoccupied, 

 and having in the synonymy " {Thyropus, Dana, Sp. Bate $ = Dithyrus Dana J, Platy- 

 ifcelus Sp. Bate ? )," of which names Dithyrus, Dana, must take precedence of Eidy^ilds. 

 In this genus both pairs of gnathopods have compound chelae, the two end-joints of the 

 hinder antennas in the male are very much shorter than the two preceding joints, and the 

 lobes of the maxillipeds (Unterlippe) are slightly concave on the inner edge. The species 

 assigned to it are — 1. ovoides, Eisso (including Platyscelus serratus, Sp. Bate ( 9 ), and 

 Tliyrojms ovoides, Sp. Bate((^)); 2. arinahis, n. s.; 3. serratus, n. s.; 4. fjlohosus, n. s. 

 In 1887 Qaus adds " E. inermis Cls. (Dithyrus Faba Dana?)." 



