256 LECTURE XII. 



the pistil, and serving to convey the pollen to the ova ; but the ova 

 afterwards escape by rupture of the ovarium, or by what the botanist 

 calls dehiscence of the seed-capsule. It is exactly so with the earth- 

 worm ; the so-called oviducts serve to convey the impregnating prin- 

 ciple to the ova, which escape into the abdominal cavity of the earth- 

 worm, by bursting through the ovarian sacs. In these sacs, however, 

 there is always found a quantity of spermatozoa in different stages of 

 development ; and accordingly the generative organs of the earth- 

 worm are open to two interpretations. The anterior organs may be 

 regarded, as by Hunter and Cuvier, as the testes, or they may answer 

 only to the spermatheca in insects ; and, in that case, the true male 

 organ may be that external spongy part which surrounds the proper 

 ovarium ; and this would not be a solitary instance of such an 

 arrangement of the essential organs of generation in the animal king- 

 dom, but one which is very common in the androgynous gasteropods. 

 However, there is much room for research and experiment to clear 

 up this difficult moot-point. 



Both the leech and the earth-worm enjoy a double or reciprocal 

 coitus ; the leech has a true perforated intromittent organ ; the earth- 

 worm has not. During the breeding season, however, two imperforate 

 appendages are developed from about the thirty-second ring ; their 

 base adheres intimately to the cellular tissue ; they have no commu- 

 nication with the genital apertures ; are developed only at the breed- 

 ing season ; and are deciduous. The second accessory organ is that 

 thickened part of an earth-worm which is situated between the thir- 

 tieth and the fortieth segments; it is called the "clitellum," and, 

 when two earth-worms are disturbed in coitu, the adhering clitella 

 are the last parts to give way. 



With regard to the dorsibranchiate and tubicolar Anellides, many 

 of these are dioecious. The sperm-sacs or testes are situated on the 

 ventral aspect, between the layers of the ventral muscles. The deve- 

 lopment of the ova is more clear and obvious; because they are com- 

 monly remarkable for the bright colour of their vitelline mass ; and 

 tlie number of ova is so great, that the ordinary colour of the anellid 

 is changed at the breeding season. Thus, in the Aphrodite cirrata, 

 Sars found that, in February, the three posterior fourths of the body 

 were of a brilliant red colour, on account of the great number of ova 

 there accumulated. Neither testes nor ovaria have external ducts ; 

 the products of both are discharged by dehiscence, into the abdomi- 

 nal cavity, and are excluded by pores situated near the base of the 

 setigerous feet. In the Aphrodite, the ova pass between the dorsal 

 scales, and there development takes place. There is but one known 

 genus of anellid that exhibits external sexual characters, viz., the 



