REPORT ON THE CRUSTACEA MACRURA. xxvii 



inner branch, on the other hand, is entirely free from these sensory appendages, and is 

 generally smooth, slender, and flexible ; it varies in length, being frequently much 

 longer than the outer flagellum, and in other species it is considerably shorter. The 

 constant presence of an organ of such simple character indicates that it fulfils some 

 permanent function, which, I believe, consists in protecting and keeping clean the mass 

 of membranous cilia attached to the outer flagellum. This idea receives support from 

 a consideration of the relative positions of the two flagella, and from the fact that in 

 Pandalus modestus, as may be seen in PI. CXIV. fig. 46, the inner flagellum has a 

 tendency to curl spirally around the outer ; when the flagella are long the membranous 

 cilia are less aggregated, extending sometimes to the very extremity. 



In the genera Palmmon, Bithynis, Lysmata, and Alpheus, the outer or primary 

 flagellum divides at a greater or less distance from its base into two branches of varying 

 length, the basal part of which carries the sensory organs, while the other part is slender 

 and unadorned. 



According to Mr. Gulland, on the inner or secondary flagellum " the arrangement 

 of the tactfle setae is the same, but there they are rather longer." x 



The Second Antennse. — The third pair of appendages consists of the second antennae. 

 These are often very large and powerful organs, frequently adapted for weapons of 

 offence. Each consists of two distinct portions, the peduncle and the flagellum. The 

 peduncle has five joints in all the Macrura excepting the Synaxidea, in which there 

 are only four, and the flagellum is composed of a series of short articub which together 

 form a long and slender flexible rod, generally gradually tapering from base to apex. 



The most simple and characteristic form of the second antennas is to be seen in the 

 Palinuridae, in which family also some of the most interesting and pecidiar features in the 

 antennas of Crustacea are exemplified. 



In Palinurus, the first or coxal joint is fused more or less perfectly .with the somite 

 to which it belongs, and with the ventral surface of the fourth mandibular somite. The 

 under surface alone of the coxal joint is calcified, and near its posterior margin stands the 

 phymacerite, a prominent tubercle, at the extremity of which is an opening closed by a 

 very thin chitinous membrane. 



This passage is in connection with the organ known as the green gland, which in this 

 family is largely developed and is lodged both within the coxal joint and posterior to it 

 within the cephalon. The function or nature of this organ has not been satisfactorily 

 determined, but its anatomy has received the attention of naturalists, chiefly in the case 

 of the Entomostracous Crustacea and the Amphipoda, and especially by Dr. Carl Grobben 

 in a memoir on The Antennal Gland of the Crustacea. 2 According to this author the 

 antennal gland is a renal organ with a saccular appendage and urinary passage. The 



1 Loc. cit, p. 161. 2 Arb. Zool. Inst. Wien, Bel. iii. Heft 1, p. 18, 1880. 



