Annelida: — tomopteris. fi33 



wall of the body. No other more special apparatus either for the 

 Circulation or for the Aeration of the nutrient fluid, exists in this 

 curious Worm ; unless we are to regard as subservient to the 

 Respiratory function the Ciliated Canal which may be observed in 

 each of the lateral appendages except the five anterior pairs. This 

 Canal commences by two orifices at the base of the segment, as 

 shown at fig. e, 6, and on a larger scale at fig. D ; each of these 

 orifices (d, a, b) is surrounded by a sort of Rosette ; and the 

 rosette of the larger one (a) is furnished with radiating ciliated 

 ridges. The two branches incline towards each other, and unite 

 into a single Canal, that runs along for some distance in the wall 

 of the body, and then terminates in the perivisceral cavity ; and 

 the direction of the motion of the cilia which line it is from with- 

 out inwards. 



493. The Reproduction and Developmental history of this 

 Annelid present many points of great interest. The Sexes appear 

 to be distinct, Ova being found in some individuals, and Sperma- 

 tozoa in others. The development of the Ova commences in cer- 

 tain ' Oerm-cells ' situated within the extremities of the Pinnu- 

 lated Segments, where they project inwards from the wall of the 

 body ; these, when set free, float in the fluid of the Perivisceral 

 cavity, and multiply themselves by self-division ; and it is only 

 after their number has thus been considerably augmented, that they 

 begin to increase in size and to assume the characteristic appear- 

 ance of Ova. In this stage they usually fill the perivisceral cavity 

 not only of the body but of its caudal extension, as shown at c ; 

 and they escape from it through transverse fissures which form in 

 the outer wall of the body, at the third and fourth segments. The 

 Male reproductive organs, on the other hand, are limited to the 

 Caudal prolongation, where the Sperm- cells are developed within 

 the pinnulated Appendages, as the germ-cells of the female are 

 within the appendages of the body. Instead of being set free, 

 however, into the perivisceral cavity, they are retained within a 

 saccular envelope forming a Testis (a, a, a) which fills up the 

 whole cavity of each appendage ; and within this the Spermatozoa 

 may be observed, when mature, in active movement. They make 

 their escape externally by a passage that seems to communicate 

 with the smaller of the two just-mentioned rosettes ; but they also 

 appear to escape into the perivisceral cavity by an aperture that 

 forms itself when the spermatozoa are mature. Whether the Ova 

 are fertilized while yet within the body of the female, by the 

 entrance of Spermatozoa through the ciliated canals, or after they 

 have made their escape from it, hasnotyet been ascertained. — Of the 

 earliest stages of Embryonic Development nothing whatever is yet 

 known ; but it has been ascertained that the animal passes through 

 a Larval form, which differs from the adult not merely in the 

 number of the Segments of the body (which successively augment 

 by additions at the posterior extremity), but also in that of the 



