146 LECTURE XII. 



convoluted oviduct, which opens upon the sixteenth segment of the 

 body. In spring the vitelline cells begin to multiply around the ger- 

 minal vesicle, in the form of minute dark specks ; towards autumn the 

 ova become red coloured, and, by their increase in size and number, 

 they render the surface of the ovarium irregular. At this season the 

 fertilising fluid reaches the ovaria by the ducts above described, which 

 are then filled with spermatozoa. The only function of the ducts is 

 to aflFord a route or jDassage to these moving filaments which, like 

 the pollen tubes in plants, attach themselves to the ova, and in such 

 numbers as, according to the observations of Dr. A. Farre, to give 

 the impregnated ova the appearance of a ciliated gemmule. The ova 

 escape, like the seeds of plants from the ovaria, by dehiscence of the 

 coats of those organs, not by passing outwards through the so-called 

 oviducts, which are analogous to the tubes in the style of a flower, 

 which give passage to the pollen filaments, but not an exit to the 

 seeds. The ova, after being expelled from the ovaria, pass into the 

 interspace between the sub-muscular membrane and the muscular 

 integument, and, by a series of strong undulations of the body, are 

 ultimately propelled to a receptacle near the arms. Here they un- 

 dergo a certain amount of development, and are frequently expelled, 

 like chrysalids, enveloped in a hard, yellow, pellucid, and slightly 

 elastic integument, probably an exuvial skin. Sometimes they are 

 expelled from the parent in this state: sometimes the young are ex- 

 cluded from their case before parturition. 



With regard to those ciliated corpuscles already alluded to, as dis- 

 covered by Dr. A. Farre, in the ovaria of the earth-worm, similar 

 bodies have been detected by Mr. Quekett in the testes of the rivulet 

 leech. They occur with more numerous unciliated spherical cor- 

 puscles, and appear to represent groups of spermatozoa, analogous to 

 the bundles in which the same filaments are aggregated in the sperm 

 sacs of the medusa. 



In the Are7iicola, or sand-worm, the testes are situated in pairs at 

 the anterior part of the body, and the ova are discharged by dehis- 

 cence of the ovaria into the abdominal cavity. 



In the genus Eunice, every segment, save the first, has its ovarium 

 and testes attached to either side, which reminds one of the multi- 

 plication of these organs in the TcenicB. The Aphroditce are stated 

 to be of distinct sexes. 



The development of the ova in the class Anellata, has been hitherto 

 but little studied. Some of tlie few observations on record in refer- 

 ence to the dorsibranchiate order, indicate that they undergo, during 

 their development, a metamorphosis almost as remarkable as that of 

 insects. Dr. Loven obtained in the month of August in the Baltic 



