CHAPTER XIV 

 ORGANS OF REPRODUCTION 



Page 



Anatomy 297 



Determinations of volume and weight of gonad _._ 299 



Histology 299 



Spawning... 303 



Spawning reaction of the female 303 



Spawning reaction of the male 310 



Frequency of spawning 312 



Fecmidity of the oyster 313 



Sex ratio, hermapliroditism, and sex change 314 



Lunar periodicity 318 



Biological significance of spawning reaction 319 



Bibliography _ 320 



ANATOMY 



The ripe gonad is a massive organ located near 

 the sm-face of the body within a layer of connec- 

 tive tissue between the digestive diverticula on 

 the inner side and the surface epithelium on the 

 other. In sexually mature oysters it appears as 

 many branching tubules (follicles) which merge 

 along the dorsal side of the body to form one 

 continuous structm-e encompassing the visceral 

 mass and extending ventrally to the tip of the 

 pyloric process (fig. 267). 



The reproductive gland is not encapsulated, 

 and its outlines are indistinct. At sexual maturity 

 the surface covering of the body becomes so thin 

 that a network of fine genital canals is clearly 

 visible through it. The diameters of the canals 

 gradually increase as they converge into a wider 

 gonoduct through which the germ cells are dis- 

 charged. Two separate systems of genital canals, 

 one on each side of the body, are the only sign of 

 the paired origin of the sex gland which in an 

 adult oyster is completely fused into a single 

 organ. 



In many bivalves sex products are discharged 

 thi-ough tlie kidneys, but in the oyster the gono- 

 duct opens into a vestibule, or atrium, which 

 also receives the urinal duct. This relationship 

 can be seen on a series of slightly slanted sections 

 of the lower part of a ripe gonad. One of these 

 sections is shown in fig. 268. The female oyster 

 from which the tissue was taken was preserved 

 dm-ing the act of spawning. The follicles of the 



FISHERY bulletin: VOLUME 6 4, CHAPTER XIV 



lower part of the ovary (left side of the figure) 

 are almost empty of ripe eggs; a short ciliated 

 passage between the ovarian follicle and the 

 pear-shaped area of the kidney vestibule are at 

 the right; two spawned eggs are near the outside 

 opening of the vestibule, which is lined with 

 ciliated epithelium. A transverse section of the 

 kidney reservoir lined with typical secretory 

 cells is in the upper right portion of the figure. 

 The connection between the vestibule and the 

 reservoir is located above this section. The 

 folUcles in the inner portion of a gonad lie at an 

 angle to the genital ducts into which tliey discharge 

 theii' content. The structure of spermary differs 

 from that of the ovary only in that the follicles 

 are filled with spermatozoa. 



The degree of sexual development can be esti- 

 mated roughly by measuring with calipers the 

 thickness of a transverse section of the gonad 

 layer. Since the gonad is not uniformly thick in 

 all its parts, the section should be made at some 

 selected place. In conformity with the practice 

 used by the Biological Laboratories of the Bureau 

 of Commercial Fisheries at Milford, Conn., Oxford, 

 Md., and Gulf Breeze, Fla., the oyster is cut with a 

 razor blade along a line extending from the lower 

 corner of the labial palps across the stomach to the 

 posterior end of the body. There is considerable 

 variability in the gonad layer of oysters of known 

 age and similar environment. In Long Island 

 Sound the average maximum thickness of ripe 

 gonads of 4- to 5-year-old oysters taken from three 

 depth levels of 10, 20, and 30 feet was, according to 

 Loosanoff and Engle (1942), about 2.4 mm. for the 

 shallow water oysters and only about L5 mm. for 

 those found in deeper water. Much gi-eater 

 gonadal development was recorded in other loca- 

 tions. Some fuUy mature Cape Cod oysters used 

 in my experimental work. had a layer of gonad 

 from 6 to 8 mm. thick, and a similar degi-ee of 

 development was noted in oysters from a small 

 tidal pool near the laboratory at Beaufort, N.C. 



297 



