Geoffrey Watkins Smith. 



xvii 



Crustacea. In a short paper " On the Metamorphosis of Gnathia " (' Mitth. 

 Zool. St. Neapel,' 1904), he corrected and completed our knowledge of the life- 

 history of this strange parasite, and shortly after lie described among male 

 TanaidcC and other Crustacea a form of high and low dimorphism comparable 

 to that already known among insects. At the request of Prof. Dohrn he 

 then undertook to write a monograph on the Ehizocephala, a group of 

 parasitic Cirripedes of extreme interest. For this purpose he remained for 

 nearly three years in Naples, and produced a monograph which, although one 

 of the shortest, is certainly one of the most interesting of the whole series. 

 Indeed, it is typical of the scientific work of Geoffrey Smith, who aimed 

 neither at encyclopedic completeness nor at the accumulation of meauingless 

 detail. Bringing to bear on the problems before him a mind of remarkable 

 freshness and originality, he attacked them from new points of view and with 

 the help of new methods, never losing sight of the main points at issue. 



Since this monograph, together with a series of " Studies in the Experi- 

 mental Analysis of Sex," published later in the 'Quart. Journ. Micro. Science,' 

 1910-14, formed his most important contribution to science, they deserve 

 special notice. The life-history of the interesting Ehizocephalan Sacculina, 

 a parasite which infects crabs, had already been worked out, chiefly by 

 Delage, and Geoffrey Smith was able not only to confirm the brillia.nt work 

 of the French zoologist, but also to complete his observations, especially with 

 regard to stages between the larva which has just penetrated into the host 

 at any point, and the young Sacculina fixed in its definitive position on the 

 intestine of the crab. Some time previously Giard had described the remark- 

 able effect produced on the host by the Sacculina, and named it parasitic 

 castration. It results in the profound modification of the sexual characters 

 of the crab, the degeneration of its testis or ovary, and the acquisition by 

 the male of the secondary sexual characters of the female. The difficult 

 problem of the feminisation of the male Smith attacked with conspicuous 

 success. He showed that the female, if parasitised young, was merely 

 made to acquire prematurely the characters of the mature adult; that the 

 male only has the capacity to acquire the characters of the opposite sex, 

 that a male individual, having got rid of the Sacculina, and recovered from 

 its attack, regenerates an hermaphrodite gonad with ova and spermatozoa. 

 This modification of the sexual characters, he argued, is related to a deep- 

 seated change in the general metabolism. In the maturing female fat 

 metabolism is very active for the purpose of nourishing the eggs, the blood 

 becomes loaded with fat and the liver stored with it. The parasite, absorb- 

 ing food-material, plays the same part in the host as the ripening ovary, 

 stimulates fat production, and thus converts the metabolism of the male to 

 the female type of metabolism. Since the secondary sexual characters 

 appear before the regeneration of the gonad, it follows that in this and in 

 many other cases the development or modification of the characters is due, 

 not to the secretion by the ovary or testis of some special hormone, but to a 

 profound alteration in the metabolism of the animal. 



