THE 3IULLKJMAN DUCTS AND REPRODUCTIVE ORGANS. 197 



eggs as they pass down the duct, and which, on reaching the 

 water, swells up to form the mass of the frog's spawn. The 

 hinder end of the oviduct remains thin-walled, but dilates very 

 greatly, forming a capacious sac in which the eggs accumulate 

 before being laid. 



6. The Reproductive Organs. 



The development of the reproductive organs has already 

 been described (p. 94), but a few further details may be given 

 here, more especially with regard to the relation between the 

 reproductive organs and the Wolffian bodies, and the develop- 

 ment of the fat bodies, or corpora adiposa. 



The reproductive organs appear in. tadpoles of about 10 mm. 

 length, as a pair of ridge-like folds of the peritoneum, lying 

 along the inner borders of the Wolffian bodies, close to the root 

 of the mesentery (Fig. 85, OH, and 87, ov). These genital folds 

 soon become more conspicuous, and undergo changes which have 

 already been described in detail, by which the germinal cells 

 or gonoblasts are formed. 



As the Malpighian bodies develop on the .tubules of the 

 Wolffian body, those lying nearest to the genital ridge give off 

 hollow tubular diverticula, which, arising from the capsules of 

 the Malpighian bodies, grow towards the median plane, and 

 into the substance of the genital ridge (cf. Fig. 87), where they 

 form the so-called tubuliferous tissue. 



So far, the processes of development are the same in both 

 sexes, but from this point differences occur. In the ovary of 

 the female the tubules of the tubuliferous tissue expand very 

 greatly, and give rise to the large axial cavities of the ovary, 

 of which there are usually about fifteen in the adult. 



In the male, the outgrowths from the Malpighian capsules 

 acquire still more intimate relations with the reproductive organs 

 than in the female, and become the vasa efferentia of the adult, 

 which convey the spermatozoa from the testis to the kidney. 

 The Malpighian bodies with which the vasa efferentia are con- 

 nected are at first perfectly normal ; but later on they undergo 

 retrogressive changes, and by the end of the first year their 

 glomeruli have disappeared, and the Malpighian bodies them- 

 selves merely remain as slight ampulliform enlargements of the 

 tubules, which have now completely lost their kidney structure 



