1908.] HERMAPHRODITISM IN AN AMPHIPOD, 4{J 



the Zoological Station ; I was thus able to procure a constant 

 supply from one locality at different times of the year. 



(2) In this species adult males can without difficulty be 

 distinguished from the young of the same sex by the characters 

 of the second pair of gnathopoda. In the adialt male the pos- 

 terior margin of the " hand " is produced to form a large sjoine- 

 like process, so that the appendage becomes pseudochelate instead 

 of subchelate as in the female. The young males up to approxi- 

 mately 9 mm. in length possess gnathopoda of the female type ; 

 as they increase in size these appendages tmdergo various modi- 

 fications, but do not become pseudochelate until maturity (13-15 

 mm.) is attained. 



Barrois (4) was the first to describe and illustrate these stages 

 in the development of the gnathopoda ; a similar series is figured 

 by Delia Valle in his monograph. 



ISTebeski has very carefully described the structure of the sexual 

 organs of Orchestia gammarelhis ; I will therefore only briefly 

 summarise the more salient features in the testis of 0. deshayesii, 

 which agrees in all but details with that organ in the first- 

 mentioned species. 



The male generative organs lie on either side of the thorax 

 above the gut and are kept in position by a packing of fatty 

 tissue. The testis itself is of a fusiform shape and extends 

 approximately from the posterior part of the second thoracic 

 segment to the anterior part of the fifth. Anteriorly it is pro- 

 duced into a longish filament which seems to serve as a kind of 

 ligament. 



'The organ is clothed externally by a layer of epithelial cells 

 with large nuclei ; inside is a cavity on the median wall of 

 which the germ-cells are situated arranged in several layers. 

 Posteriorly the testis is directly continuous with the narrow 

 anterior end of the oval vesicula seminalis ; in this respect the 

 generative organs of this species differ from those of Orchestia 

 gainmarelhts where, as described by Nebeski, the posterior narrow 

 prolongation of the testis opens into one side of the vesicvila 

 seminalis a short distance behind its anterior termination. The 

 vesicula seminalis communicates with a narrow ejaculatory duct 

 which leads to a small chitinous penis situated at the base of the 

 seventh thoracic leg. 



Whilst at Naples I dissected a number of adult males of this 

 species at intervals during the months October to March, and 

 found the testes to be perfectly normal in 135 out of 137 

 individuals so examined. The two abnormal specimens possessed 

 a few small ova at the anterior end of the testis, just below the 

 origin of the ligament-like filament. Both of these were obtained 

 during the second week of October together with females carrying- 

 ova ; breeding was therefore still in progress. 



A smaller number (47) of large male Orchestia gammarellus 

 were also examined by me, but none were found exhibiting any 



