^277. 



THE CRUSTACEA. 



325 



§277. 



The sense of Sight is present quite universally with Crustacea. ^^ 



The Cirripedia, the Penellina, and the Lernaeodea, alone, are without it ; 

 and even here this deficiency occurs only during the last phases of their re- 

 trograde metamorphosis, when these animals remain fixed to foreign bodies/^' 



There is, moreover, in the other oi'ders, here and there a genus which 

 contains blind individuals. Such is the case with the females of certain 

 parasitic Lsopoda,*"^ and with some subterranean Myriapoda.*'*' 



The eyes of Crustacea present very various grades of development. The 

 lowest of these is seen in the so-called Simple-eyes. With these, there is 

 observed a convex cornea, and, behind it, a round, light-refracting body. 

 This lens is surrounded by a layer of black, brown, red, or blue pigment, 

 which, at its most convex point, is perforated by an optic nerve. The 

 youngindividualsof the Cirripedia, the Penellina, and the Lernaeodea, have 

 an eye of this kind in the middle of their forehead, but which gradually dis- 

 appears in the course of their metamorphosis.^^' Certain Ergasilina, as 

 likewise the Lophyropoda and Phyllopoda, have, also, at their escape from 

 the egg, a simple eye, which, with the Ergasilina, and certain Lophyropoda, 



thought them comparable to a cochlea, but he was 

 unable to find any nerve going to them, and has 

 relinquished this idea, — doubting that these organs, 

 and the ampulla mentioned, are really auditive or- 

 gans. Farre (loo. cit.) has gone further ; he has 

 taken these bodies for olfactory organs, and has 

 endeavored to show, as already mentioned, the or- 

 gans of smell to be real organs of hearing. It is 

 true that, in the organs of hearing, no otolites are 

 found ; but the principal parts exist, such as a Ca 

 vum tympani, at the entrance of which is extend- 

 ed a tympanitic membrane and an auditive vesi- 

 cle, upon which is spread a nerve. 



The view of Frey (De Mysidis Anat. p. 13), 

 then, is inadmissible ; he regards the seat of hear- 

 ing, with My sis, as the two internal caudal valves, 

 wfiere he has observed a cavity containing a radi- 

 ated body, the nucleus of which has a crystalline 

 structure, and which he regards as an otolite. 

 But, aside from the singular structure of this body, 

 he does not mention its having any special nerves. 



It is, moreover, unnecessary to seek, with those 

 Crustacea whose antennae are highly developed, 

 the auditive organs anywhere but on the head ; 

 for, at the base of these antennae, as, for example, 

 with the Amphipoda, there are several other hol- 

 low processes which, in part, have been regarded 

 as palpi, but which, upon more careful examina- 

 tion, will undoubtedly be found to be, some auditive, 

 and others olfactory organs. 



Frey and Leuckart (Beitr. p. 114, Taf. II. fig. 

 18) have, from the first, described in more detail 

 the organs of the caudal valves of Mysis, as 

 proper auditory organs ; but, aside from the two 

 so-called otolites which, contrary to all analogy^ 

 are provided with stiff bristles, the correctness of 

 this nterpretation is always open to question, for 

 these authors have been unable to perceive any 



nerve destined for these so-called auditive capsules, 

 with Mysis. 



1 For the eyes of Crustacea, see especially J. 

 Müller, Zur vergleich. Physiol, d., Gesichtsinnes, 

 p. 307 ; or its abstract in Ann. d. Sc. Nat. XVII. 

 1829, p. 225, or his later researches on the eyes of 

 the Insecta and Crustacea, in Meckel's Arch. 

 1829, p. 38, and in Tiedemann's Zeitsch. f. Phys- 

 iol. IV. p. 97. 



2 The adult Cirripedia, notwithstanding the ab- 

 sence of eyes, are very sensitive to light. This I 

 have observed with individuals of Balanus pxisil- 

 lus, which I had captive several weeks at Danzig. 

 These animals, when undisturbed, came out of their 

 shell, and executed the usual motions of their cirri, 

 but they withdrew as quick as lightning into the 

 shell, when, from passing my hand over the vessel, 

 I shaded them. Coldstream (Cyclop, loc. cit. p. 

 688) has made similar observations.* 



3 The fanaXeti of Jone, Phryxus, and. Bopyrus.\ 

 i For example, with Polydesmus, Blaniulus, 



Cryptops, and Geophilus. 



5 For example with Achtheres, Tracheliastes, 

 Lernaeocera (Nordmann, loc. cit. p. 80, «'&c., 

 Tab. IV. fig. 5, Tab. VI. fig. 5, 6). The Cirripe- 

 dia have, at their escape from the egg, a single, 

 black eye, according to Thompson ; see the PhUos. 

 Trans. 1835, p. 355, Owen, Lectui-es, &c., p. 161, 

 fig. 88 ; and Goodsir, Edinb. new Philos. Jour. 

 1S43, No. 69, p. 97, PI. III. fig. 8, and PI. IV. fig. 

 13-17 {Lepas and Balanus); but with the embry- 

 os of Balanus pusillus, I have found this eye of 

 a red color. The reason why Burmeister (Beitr. 

 &c. p. 15, Taf. I. fig. 2) could perceive no eye 

 with the young of Lepas, is, as he himself has re- 

 marked, because they had been effaced by the 

 alcohol in which the specimens examined had 

 long been preserved. 



* [§ 277, note 2 ] Recent investigations have 

 disclosed the existence of eyes with the Cirripedia. 

 Leidy (Proceed. Acad. Sc. Phil. IV. 1848, No. 1) dis- 

 covered them with Balanus, and this discovery has 

 led to the confident and successful search of them 

 in other genera. With Lepas, according to Dar- 

 win (Monograph, &c., loc. cit. p. 49), there are two 

 cloaely-approximated eyes, forming a double eye, 



28 



situated at the extremity of two optic nerves which 

 proceed each from an ophthalmic ganglion. These 

 ganglia are situated on two nervous cords which 

 arise from the supra oesophagearl ganglia. — Ed. 



t [ § 277, note 3.] Quite remarkable among the 

 blind Crustacea is the Astacus pellucidus Telk. 

 from the Mammoth Cave, Kentucky. — Ed. 



