ENDOCRINOLOGY OF CRUSTACEANS 177 



X-organ and the sinus gland constitute an anatomical complex, connected 

 to each other by way of the so-called sinus-gland nerve (Bliss and Welsh, 

 1952; Passano, 1951a; but see also Enami, 1951, and Gabe, 1954). Accord- 

 ing to the hypothesis elaborated by Passano, the fibers of the sinus-gland 

 nerve are axons arising from the neurons that make up the X-organ, and 

 the secretory products of the X-organ cells are transmitted along the fibers 

 of this nerve to the sinus gland ; the sinus gland is considered to consist 

 principally of the free axon endings which have been distended by the 

 accumulation of the neurosecretory product. 



While the studies cited above have resolved some of the apparent con- 

 tradictions of the earlier investigations of the hormonal basis of molting in 

 crustaceans, even more recent experiments have indicated that additional 

 hormonal mechanisms may be involved. Carlisle and Dohrn (1953) postu- 

 lated the existence within the eyestalk of a molt-accelerating hormone for 

 which they proposed the name of growth hormone or somatotrophin. Their 

 conclusions were drawn from experiments which consisted of the injection 

 of a variety of extracts into Lysmata during the winter when the normal 

 molting rate of this animal is low. The highest molt rates (and also mor- 

 tality among injected animals) were shown by Lysmata injected with 

 human chorionic gonadotrophin, mammalian posterior pituitary extract, 

 and extract prepared from the eyestalks of female Lysmata collected in the 

 summer. The effective molt-inducing properties of the remaining injected 

 substances were, in descending order: extracts prepared from the eye- 

 stalks of female Palaemon collected in summer ; uninjected controls ; boiled 

 extract prepared from eyestalks of female Lysmata collected in summer ; 

 extracts prepared from eyestalks of male Lysmata collected in summer ; 

 extracts from eyestalks of Lysmata collected in winter ; and acidulated 

 distilled water — but the differences among these last five groups are 

 probably not significant. Because of the high mortality among their ani- 

 mals, Carlisle and Dohrn subjected their results to a statistical probit 

 analysis for determining the significance of the data from their experi- 

 mental and control groups. The possibility exists, however, that they may 

 have been measuring a nonspecific chemical efi^ect of injected substances. 

 In subsequent studies, Carlisle (1953a) reported that the molt-accelerat- 

 ing effect could be obtained by feeding animals eyestalks from donor ani- 

 mals and by a single injection of extract (equivalent to three eyestalks). 

 Some unanswered questions arise concerning the dift'erences in effective- 

 ness of extracts prepared from the eyestalks of males as against those pre- 

 pared from females, and whether implants of equivalent amounts of eye- 

 stalk tissue might not have given more striking results than a single injec- 

 tion of eyestalk extract. 



Two later reports by Carlisle (1953c and 1954) are in striking con- 



