WHITE SHRIMP FROM THE GULF OF MEXICO 



137 



These distal optic ganglia do not show super- 

 ficially; however, longitudinal sections indicate 

 very clearly the presence of a proximal, medial. 

 and distal ganglion. If the distal optic gan- 

 glionic mass is pulled away from the dioptric 

 elements of the eye, the tearing is confined to 

 natural lines of weakness representing a deep 

 concavity. Lining the concavity so produced is 

 the capillary arbor (fig. 9), a structure which 

 will be treated more fully in the section on the 

 circulatory system. 



NEUROHORMOXAL ELEMENTS 

 ' Figure 10 



Along the lateral side of the optic tract, and 

 embedded in the perineurium in the proximal 

 region of the optic tract, is a small nerve which 

 branches out of the perineurium distal to the basal 

 segment of the eyestalk. This nerve puts out sev- 

 eral tiny branches to muscles and then enters a 

 glandlike structure previously identified by 

 Young (1956) as the X-Organ (fig. 10) of 

 Hanstrom (1948), and which should be referred 

 to as the pars ganglionaris X organi (Carlisle 

 and Passano, 1953) rather than the X-Organ of 

 Hanstrom. 



From the pars ganglionaris X organi, a nerve 

 continues along the optic tract distally to enter 

 another, and larger, glandlike organ termed the 

 ''sinus gland" (fig. 10). The sinus gland lies 

 against and sends branches into the optic gangli- 

 onic mass at the distal end of the optic tract. A 

 second part of the X-Organ, that described by 

 Hanstrom, is associated with the anterior eyestalk 

 pore, or sensory pore (fig. 10). Knowles and 

 Carlisle (1956) have proposed the term sensory 

 pore X-Organ for the structure, to distinguish it 

 from the ganglionic part. The identification of 

 the parts of the X-Organ and of the sinus gland 

 was made on doubtful grounds, since no support- 

 ing histological or experimental evidence was 

 presented (Young 1956). 



Confusion surrounding the identification of the 

 X-Organ may be found in the literature of neuro- 

 secretory experiments (Knowles and Carlisle. 

 1956). Evidently the European and American 

 workers have used the term "X-Organ" for dif- 

 ferent structures. The reason may lie in a weak- 

 ness in communications, for the illustrations 'in 

 some works of this literature are, to say the least, 

 circumscribed (Passano 1953), however impor- 



tant the textual material may be to the experi- 

 mental biologist. Welsh (1941), on the other 

 hand, has taken pains to illustrate clearly his 

 experiments on retinal pigment migrations in 

 Garribarus iartoni (Fabricius 1798); unfortu- 

 nately his identification of the X-Organ appears 

 to be in error. 



Keim (1915) in his account of the nerves in 

 Astacus does not illustrate the sinus gland or the 

 parts of the X-Organ. 



OCULOMOTOR NERVE 



Figures 8, 9. 10 



The oculomotor nerve originates on the lateral 

 side of the dorsal brain, slightly posterior to the 

 optic tract, and, beginning ventrally, describes an 

 almost complete loop around the protocephalon 

 attractor muscles. It proceeds to the dorsolateral 

 region of the protocephalon attractor, between 

 the muscle and the outer epidermis. From the 

 latter position the nerve turns sharply anterior 

 and runs into the eyestalk, giving off branches to 

 various of the eyestalk muscles. The nerve in 

 Penaeus is the same as the eye muscle nerve de- 

 scribed by Keim (1915) in Astacus. 



Kegrettably, very little can be said of homolo- 

 gies between the nerves serving the eyestalk of 

 the various Crustacea, since so little information 

 exists on the subject. Certainly, optic tracts, ocu- 

 lomotor nerves, and eyestalk neurohormonal ele- 

 ments in Penaeus, Astacus, and Canibarus are 

 likely to be homologous structures. Further ana- 

 tomical information on the nerves will have to be 

 provided before the comparative morphology of 

 this region of the brain and eyestalk will be in 

 any way a satisfactory story. 



AXTEXXULAR XERVES 



Figures 14, 15, 75, 76 



The nerves of the antennule pass rostrad from 

 the anteroventral region of the supraesophageal 

 ganglion within a single perineurium. Inside the 

 antennule the single tract divides into three 

 nerves. The largest is the short, flat statocyst 

 nerve which runs anterolaterally and spreads 

 widely on the ventral surface of the first antennu- 

 lar segment beneath the statocyst. This nerve is 

 presumably the sensory nerve of the statocyst. 

 The smaller antennular nerves parallel the stato- 

 cyst nerve in the proximal region of the anten- 



