THE GONOSOME. 



53 



On laying open the gonan 

 a blastostylc [d), which gives 

 origin to one or more gono- 

 phores. It terminates upwards 

 by closing round the distal ex- 

 tremity of the blastostyle, where 

 it forms a ring (/) with tooth- 

 like processes, l)y which the 

 extremity of the blastostyle is 

 encircled. This oval portion 

 constitutes the gonangium pro- 

 per, and is the only part deve- 

 loped in the male (fig. 20 a). 



From the summit of the 

 blastostyle three tentacula-like 

 processes {//) arc given off. 

 They constitute ramified cffical 

 offsets of the cavity of the 

 blastostyle, and are composed 

 of an ectodermal and an endo- 

 dermal layer. Immediately 

 after their origin from the 

 blastostyle they enter the ter- 

 minal leaflets, and now lie 

 between the two lamiua3 of 

 which these leaflets are com- 

 posed. 



The leaflets, with their 

 contained csecal oSsets from 

 the blastostyle, surround a 

 membranous sac (0 which is 

 borne on the summit of the oval 

 portion, or proper gonangium, 

 and contains one or two ova, 

 which are usually in an ad- 

 vanced stage of development. 

 Each ovum is immediately in- 

 vested by a delicate structure- 

 less sac (/•), which is continued 

 by a neck-like prolongation to 

 the summit of the blastostyle.' 



The homological relations 



gium the oval or proximal portion of it is seen to be occupicxl by 

 Fig. 2(5. 



Male and female gonangia of Sertularia tamarisca. 

 A, Male gonangium ; B, female, with its marsupial chamber. 



a. Proper gonangium ; b, blastostyle with c, its opercular summit; d, gubernacu- 

 lum ; e, gonophores, having the spadix surrounded by the spermatozoa in the male 

 and by the ova in the female ; fy chitinous roof of the gonangium proper in the 

 female, perforated by a central denticulated aperture ; g^ g\ g'\ the three leaflets, 

 forming the walls of the marsupial chamber, and each containing within it a rami- 

 tied ca?cal process, h, from the summit of the blastostyle; g'' is cut across and de- 

 ", acrocystftl sac ; A", ovum, included in a special sac. 



The account here given of the marsupial receptacle of Sertularia tamarisca differs in some 



