Dr. T. Williams on the Reproductive Organs of the Annelids. 395 



organs remain in the condition of simple * discharge tubes,' while 

 others become developed into the Reproductive structures. 



The segmental organs of the Hirudinaceae are next described. 

 The author adheres almost in every detail to the results published 

 by him in 1 85 1 in the Reports of the British Association, with re- 

 ference to the reproductive system of this family of Annelids. In the 

 present memoir he records the results of new and carefully conducted 

 dissections, which prove that in the Common Leech, the Sea-leech, 

 and probably in the genus Clepsina, there is situated an organ on 

 either side of the ventral median line, which is repeated in every ring 

 of the body^ and which in this family is the true ovigerous apparatus, 

 the testes constituting a separate and more medianly disposed series 

 of glandular bodies, whose homologies he has not yet satisfactorily 

 determined. 



The so-called " respiratory sacculus " of Duges he now looks upon 

 as the process of the ovario-segmental organ, by which a communica- 

 tion is established between the latter and the general cavity of the 

 body, and by which the fluid of this chamber escapes externally. 

 All the Hirudinaceae are androgynous. 



Under the Nereid group is included in this memoir, the genera 

 Nereis, Aricia, Phyllodocey NephthySy Syllis and Nerine. The 

 segmental organ in these families is specially described and figured. 

 In all, the sexes are seated on separate individuals. In no single in- 

 stance is the general cavity rendered subservient to the incubatory 

 process. In all, the general circumference of the organ is lobulated 

 and irregular, entering the hollow bases of the cirrhi and blended 

 most intimately with the blood-vascular system. 



Glycera and Cirrhatulus the author classes together, on account 

 partly of the similarity of form and structure of the segmental organ, 

 but especially because in both the blood-vascular system is completely 

 and entirely wanting , its absence being compensated by the existence 

 of a second order of pigment-carrying corpuscles in the cavitary fluid. 

 These genera are unisexual, and at no time are the germ- and sperm- 

 elements introduced into the perivisceral chamber. 



In this and the preceding groups the author has not succeeded in 

 discovering the mode in which the segmental organ opens into the 

 general cavity ; but from the fact that it has a looped arrangement, 

 supported on two tubular limbs, he is quite convinced that an open- 

 ing into this cavity, for the purpose of giving direct outlet to its con- 

 tents, does really exist. This conclusion is fortified by the analogy 

 of the form under which the organ exists, in the Nereid group in 

 general. 



The Nemertine Annelids are then examined. The author recalls 

 the results of his researches as published in his * Report ' on the 

 Annelids in 1851. His renewed investigations have confirmed the 

 statements which he then put forth. He still contends that what 

 M. Quatrefages has described in these worms as the ovary is a great 

 alimentary caecum., and that the Reproductive system consists in a 

 double series of segmental organs, one on either side of this great 

 caecum and the ventral median line ; that in this family the sexes are 



