ENDOCRINOLOGY OF CRUSTACEANS 179 



A series of three recent short papers has presented evidence for another 

 hormone which is concerned with molt. A paper by Gabe (1953) reported 

 the presence in a variety of crustacean species of a structure which is named 

 the Y-organ, located in the antennary or maxillary metamere ; this struc- 

 ture has a highly secretory appearance during stage D of the molt cycle, 

 and Gabe therefore postulated that it might be concerned with the molt 

 process. Echalier (1954, 1955) undertook an experimental study of the 

 role of the Y-organ in the molt cycle of Carciniis, and his first reports indi- 

 cate that removal of the Y-organ results in a block in the development of 

 the usual sequence of stages of the intermolt period : 50 young animals 

 serving as controls had molted once within a two-months period and either 

 had molted a second time or were close to the second molt ; of 90 experi- 

 mental animals from vvhich the Y-organ had been surgically removed, 68 

 had not molted ; of the 22 operated animals which did undergo molt, 10 

 had been operated in stage Do, very close to the approaching normal molt, 

 but were blocked in stage C of the following intermolt period. When 3-4 

 pairs of Y-organs were removed from donors and were implanted into 

 Carcinus which had been without Y-organs, 6 survived the implantation 

 and two of these resumed the normal intermolt cycle and molted 40 days 

 after the implantations. While the number of experimental animals cited 

 in this second report is small, and may represent only a preliminary study, 

 the evidence is qualitatively such that the presence of an accelerating hor- 

 mone from the Y-organ may be added to the inhibiting hormone from the 

 X-organ-sinus gland complex to constitute the crustacean endocrine arma- 

 mentarium for molting. 



How such a double set of hormones for the regulation of molting is 

 physiologically employed is still unknown. Our knowledge of the coordi- 

 nation of physiological mechanisms in molting, despite the wealth of mor- 

 phological and physiological details of the process, is still amazingly super- 

 ficial. The trigger mechanism to molt is unknown. We have only some 

 slight indication that feeding or nutritional state, daily photoperiod 

 (Stephens, 1955), and temperature may play a role in the process; but 

 how these internal and external environmental conditions, along with the 

 more complex metabolic phenomena of molt, may interplay with the hor- 

 mones involved, and how the initiation and cessation of secretion of these 

 hormones may be regulated are still largely obscure. We might be justified 

 in predicting that secretion of the molt-inhibiting and the molt-accelerating 

 substances must be interrelated ; for it would otherwise seem physio- 

 logically uneconomical to have two opposing regulatory devices partici- 

 pating in so slow a physiological process as molting. 



The neurosecretory complex of sinus gland-X-organ will undoubtedly 

 be the subject of additional study, since it is apparently the basis not only 



