THE GONOSOME. 



G5 



Fig. 31. 



frequently contained as a brood in the interior of mother-cells, as may he very well seen in 

 Sertidariapoli/zoiiias, where the cells which give immediate origin to the spermatozoa form groups 

 of from two to four enclosed within a common mother-cell. The spermatozoon itself seems due 

 to the metamorphosis of the nucleus of the sperm-cell. 



In Laomedea Jlexuosa I have carefully followed the progress of the spermatogenous tissue from 

 a very early period to the formation of the mature spermatozoon. In the very young gonophore 

 of this hydroid (woodcut, fig. 31 A) the spadix may be seen . surrounded by a nearly transparent 

 mass, which is destined to become 

 developed into spermatozoa, but which 

 presents as yet no obvious structure 

 beyond a minutely granular condition, 

 which under the action of acetic acid 

 becomes more distinct. 



In a stage a little further advanced 

 (B) the gonophore has increased in size, 

 and the spermatogenous mass has 

 become more voluminous and has ac- 

 quired a manifest structure, being now 

 plainly formed of a peculiar tissue 

 which, when liberated from the con- 

 finement of the gonophore and spread 

 over the field of the microscope, is 

 seen to consist of a multitude of bodies 

 of a rather irregularly pyriforui or 

 conical shape, and about j^th of an 

 inch in diameter (D a). These bodies, 

 when set free, present for the most 

 part an evident vibratory movement, 

 which seems distinct from mere mole- 

 cular motion, though as yet no filament 



or other source of the motion can be detected. When treated with acetic acid, they assume a 

 regularly spherical form, and have then all the appearance of thick-walled cells with an undoubted 

 nucleus in their interior (D b). 



In a more advanced stage the contents of the gonophore have still further increased in 

 opacity, and are now seen to be entirely composed of very minute spherical corpuscles (D c) about 

 go^th of an inch in diameter, and presenting a close resemblance to the nuclei of the cells 

 composing the spermatogenous tissue in the stage last described. They exhibit distinct but 

 not active motion under the microscope, though no filament can as yet be demonstrated in 

 them. 



In the next stage (C) the gonophore has attained maturity, and the spermatogenous mass 

 has become still more opaque than in the preceding stage, and presents a peculiar striated 

 appearance, the striae radiating from the sides of the spadix to the walls of the gonophore. Soon 

 after the gonophore has attained this condition it bursts, and allows its contents to escape into 

 the surrounding water as mature active spermatozoa (D d). These spermatozoa have an ovo- 



9 



6'0 



Development of tlie Spermatozoa iu Laomedea Jie.rv.osa. 



A, Very young male gonopliore, showing the spermatogenous plasma 

 interposed between the ectoderm and the endoderm. 



B, Gonophore further advanced. 



C, Mature gonophore. 



D, Structure of spermatic tissue at various stages ; a, spermatic tissue 

 from B ; b, the same after treatment with acetic acid ; c, spermatic tissue, 

 from a gonophore somewhat further advanced tlian B; rf, mature sperma- 

 tozoa from C. 



