REPORT ON THE CRUSTACEA MACRURA. 



XXlll 



thalmous Crustacea ; the hairs are found in the young, though in less numbers than in 

 the adult, and similarly, they are more numerous in the higher than in the lower forms. 

 Although there seems to be no doubt that these organs respond to stimuli which are 

 something else than tactile, we are not yet in a position to definitely assert that they have 

 an olfactory function. The author concludes by remarking that the character of these 

 parts has a value for the systematise That all parts have a value for the systematist is 

 true, but I can find little that is trustworthy in the appearance of the membranous cilia, 

 or sufficiently distinct and constant to assist in the determination of species. It has been 

 shown that these membranous rods exhibit distinct variations of form in certain different 

 species ; but it is equally certain that a large number of very distinct species have them 

 of precisely similar form, and they are there- 

 fore valueless as a guide for the determination 

 of specific alliance, although in some instances 

 their variation is distinct in closely allied 

 forms. 



In the genus Palinurus the flagella are very 

 short and the outer one is robust (Fig. VI., b') 

 when compared with the inner. It commences 

 with a long and narrow articulus at the base, 

 obliquely attached to the peduncle ; the second 

 is shorter and a little broader, the next four 

 or five are gradually broader but irregularly 

 longer, after w r hich they decrease much in 

 length, especially on the outer side, so as to 

 produce a curve in the flagellum ; then the 

 articuli gradually narrow towards the ex- 

 tremity, where they become slightly elongated. 

 From the commencement of the shortening 

 articuli to those at the distal extremity the 

 inner surface is flattened (Fig. VI., b"), the 

 margins of the depressions being furnished with 

 a row of long, straight, stiff, sharp-pointed spines, those on the one side being cdiated, 

 those on the other smooth, and between the two there is a thick mass of membranous 

 cilia that are much shorter than the marginal spines. These membranous cilia have 

 the walls of extreme tenuity, and parallel to a considerable extent, when they suddenly 

 narrow to a long and slender point (Fig. VI., V") ; these organs when treated with caustic 

 potash exhibit an articulate structure in the body of the cilium, but in the slender 

 extremity a delicate spiral condition exists. 



In the genus Panulirus, where the flagella (Fig. VII.. b') of the first pair of antennae 



Fig. VI. — Palinurus vulgaris — b', outer flagellum; i", section 

 of outer flagellum; V", distal extremity of a sensory cilium. 



