272 ANNELIDA. 



apparatus, both in the males and females, is restricted to the abdominal 

 portion of the body. According to this distinguished anatomist, the 

 testicle consists of a kind of areolar web of extreme delicacy, which, 

 arising from a median aponeurosis, adheres to the internal and inferior 

 surface of the general cavity, rising as high as the middle of the di- 

 gestive canal. The tenuity of this tissue is such that it is impossible 

 to procure more than small fragments for microscopic examination. 



(696.) The ovary is in every respect similar to the testicle : perhaps 

 its texture may be rather firmer, but not sufficiently so to be adapted 

 for satisfactory histological distinction. 



(697.) In the males as well as in the females, but more especially in 

 the latter, during the period of reproduction a pigment is secreted in 

 great abundance, which lines the generative organs ; but in proportion 

 as the ova or zoosperms become developed, the amount of this pigment 

 diminishes. Both the ovary and testicle are evidently temporary organs, 

 no traces of them being distinguishable in the generality of specimens ; 

 and moreover, in proportion as their products become developed in the 

 general visceral cavity, they become gradually atrophied. When the 

 male secretion is at maturity, a jet of water washes away the sperma- 

 tozoids, and no trace of the testicle is left ; on the contrary, when the 

 sperm is immature, washing still leaves behind a delicate web almost 

 resembling a light cloud. 



(698.) The segmental organs in the genus Terebella, in all essential 

 particulars, agree in their general structure with those of Arenicola. 

 They diifer in number in different species : thus, in Terebella nebu- 

 losa there are sixteen pairs, in T. conchilega only six, and in T. multi- 

 setosa twenty-four. The testes in the male Terebella, according to 

 Dr. Williams, are the lateral pouches or true segmental organs ; in the 

 female, these are the ovaria : the generative products in both sexes are 

 early introduced into the general cavity, in the fluid of which they 

 become rapidly developed. There exists, however, in the TerebellaB a 

 large glandular mass extending from the head, along the median line, 

 to some distance in the direction of the tail. This glandular-looking 

 organ coincides internally with the smooth, foot-like, dense tegument- 

 ary structure observable on the thoracic half of the abdominal aspect 

 of the body externally, and has been described by Cuvier, Milne - 

 Edwards, De Quatrefages, Grube, Stannius, and others as the testes. 

 It would seem however, from the researches of Dr. Williams, that they 

 have nothing to do with the generative system. They are present alike 

 in the male and in the female. They consist of follicles filled with large 

 fatty particles; and their office seems to be to supply the lubricating and 

 cementing fluid by which the animal forms and moulds its tube. 



(699.) In these Erratic Annelidans, according to M. de Quatrefages *, 

 the eggs, as well as the spermatozoids, which exist in a very rudimentary 

 * " Sur le Sang des Ann&ides," Ann. des Sci. Nat. 1846. 



