70 BULLETIN OF THE 



as smooth. The absence of facets from Amphipods is naturally ac- 

 counted for by the absence of a definite arrangement among the cells 

 of the corneal hypodermis. 



In the genus Tenais, the systematic position of which is probably 

 somewhere between the Amphipods and Isopods, the corneal cuticula is 

 stated by Muller ('64, p. 2) to be facetted, at least in the males. Ac- 

 cording to Blanc's ('83, p. 63.3) more recent observations, however, it is 

 claimed to be unfacetted. 



The cones in Amphipods have long been known to be segmented. 

 The number of segments of which each cone is composed has been dif- 

 ferently stated, however, by different observers. According to Clapa- 

 rede ('60, p. 211), the cones in Hyperia are each composed of four seg- 

 ments. This also is the number given by Sars ('67, p. 61) and by 

 Leydig ('79, p. 235) for Gammarus. Both Hyperia and Gammarus 

 have since been carefully studied, and these observations are now 

 known to be inaccurate. Claparede was perhaps influenced in his 

 statement by his belief that all cones were composed of four cells. 

 Sars was probably misled by the supposed fact that in Gammarus the 

 cone is surrounded by four bands of pigment, which sometimes give it 

 the appearance of being divided into four segments. 



The actual number of segments in the cone of Amphipods is two. 

 This number was first recorded by Pagenstecher ('61, p. 31) for the 

 cones of Phronima. Pagenstecher believed, however, that the cones 

 in this Crustacean increased in numbers by division, and that they 

 showed no indication of being composed of two segments except when 

 they were undergoing this process. I need scarcely add that subse- 

 quent investigations have not confirmed Pagenstecher's belief. Cones 

 composed of two segments have been observed in some six or seven 

 genera of Amphipods. 1 



The retinula in Amphipods is stated by different observers to consist 

 of either four or five cells. Five have been seen by Grenacher ( ; 74, 

 p. 653) and Carriere (85, p. 160) in Hyperia; by Grenacher ('79, 

 p. 11.2), Claus ('79, Taf. VIII. Fig. 65), and Carriere ('85, p. 164) in 

 Phronima; and by Mayer ('82, p. 122) in Caprella. 



In Gammarus, Sars ('67, p. 61) observed that the cone had four 



1 In Caprella (Mayer, '82, p. 122), in Gnmmarus (Grenacher, '70, p. 110, Car- 

 riere, '85, p. 156), in Hyperia (Grenadier, 74, p. 652), in Oxj/cephalus (Claus, '71, 

 p. 151), in Phronima (Schmidt, '78, p. 5, Grenacher, '79, p. 112, Claus, '73, p. 130), 

 in Talorchestia (Watase, '90, p 296), and in the Piatyscclidic (Claus, '87, p. 15). 

 In Gammarus omatus, Talorchestia longicornis, and Caprella, each cone is composed 

 of two cells. 



