162 Transactions. — Zoology. 



smooth while that of Astacus being " rough with irregular prominences, is 

 something like brainstone coral." The gastroliths of Paranephrops are 

 usually pale blue in colour. 



The facts with regard to the occurrence of the gastroliths in the speci- 

 mens of Paranephrops setosus that I have examined are as follows : — First 

 specimen, male, caught October, 1880 (i.e. in the Spring), ecdysis had 

 taken place shortly before this animal was caught, for the shed gastric 

 armature was found in the stomach, the exoskeleton, however, was moder- 

 ately hardened — the gastroliths were very large : second specimen, male, 

 caught about the middle of April, 1881, gastroliths rather small: third 

 specimen, female, caught shortly afterwards, gastroliths absent : fourth 

 specimen, female, caught May, 1881 ; in this specimen ecdysis had taken 

 place shortly before its capture, the integument was thin and scarcely 

 hardened and the shed gastric armature and membrane were found in the 

 stomach, gastroliths very large : fifth specimen caught later on in May, no 

 gastroliths. Three other specimens were obtained in September, 1881 

 (i.e. early in Spring), of these in two the gastroliths were present though 

 very small, in the third there were no gastroliths. It is therefore evident 

 that the development of the gastroliths in Paranephrops setosus must differ 

 from that in Astacus fiuviatilis. 



The liver is large and yellow in colour, but it does not appear to differ 

 essentially from that of Astacus. 



The green gland as in Astacus consists of two portions, first the gland 

 which is green in colour and communicates with the second part, the sac, 

 which has extremely delicate whitish walls and opens at the base of the 

 antenna (pi. XIX., fig. 2, gg). When examined microscopically the gland 

 is seen to contain granular cells, but I did not make out the " much convo- 

 luted tube " of Lezdig.* 



Nervous system and sense organs. — The main portion of the nervous 

 system, viz., the chain of ganglia on the ventral aspect of the body, appears 

 to closely resemble that of Astacus. 



Eye. — As in Astacus the cornea of the eye is "divided into a great number 

 of minute usually square facets, by faint lines, which cross it from side to 

 side nearly at right-angles with one another."! I have not studied the 

 internal structure of the eye. 



The auditory sacs, which are situated in the basal joint of the antennules, 

 closely resemble those of Astacus, and the auditory hairs from them are ex- 

 ceedingly like the one figured by professor Huxley.} 



* See " The Crayfish," p. 353. 



t " The Crayfish," p. 118-9. 



I " The Crayfish," p. 117, fig. 27, B and C. 



