On the generative Orjcans aiiJ I'rotluits of Tomopteris onisiiformis K. 441 



in T. onisciforiniSy but Quatrkfaues saw only one pair in the fourth 

 segment and suggested that they were "pores génitaux". Apparently 

 they were not again seen till Gukeff observed them in T. rolasi and 

 T. mariana and he figured both pairs in the latter (tab. 12, fig. 4). 

 The hyaline nature of the animal, as well as its continual activity 

 and restlessness, make it ilifticult to distinguish them in the living 

 animal, especially on the ventral surface, and it was only after my 

 specimens were fixed, stained, and mounted, that I could see them. 

 1 was fortunate in obtaining examples of ditierent ages, and conse- 

 quently of varying maturity, and so was able to trace the development 

 of the orifice from a very early stage, up to the point where the 

 aperture is distended for the extrusion of the generative products. 

 In some, even with ova nearly ripe, it was impossible after careful 

 search to distinguish the opening, but the negative result was probably 

 due to too deep staining or lack of difi'erential staining of the whole 

 mounts. I can therefore appreciate the difficulty which previous ob- 

 servers, who tried but did not find the openings, experienced. Once 

 however the orifice in the fully mature individual is seen, it is easier 

 to trace its development in younger forms. 



In the youngest form, in which the tissue destined for the form- 

 ation of the aperture was seen (Fig. 33 /". o.), the paired tissue on 

 opposite sides in the same segment was not connected together across 

 the middle line, as is shown in older individuals. The apertures were 

 still shut and, as Gkeeff has noticed in T. rolasi and T. mariana, 

 they ran diagonally across the body outwards and forwards. They 

 are situated about mid-way between the middle ventral line and the 

 anterior point of origin of the lateral appendage. In preserved spe- 

 cimens each seems to consist of a band of tissue with elongated 

 nuclei ; the band separates in the middle and becomes united at either 

 end, mb. The space left by the division of the band is spindle-shaped 

 and not unlike the shape of the opening ultimately formed. The 

 cells composing the l)and are not much elongated, and the nuclei 

 occupy the greater parts of the cavities of the cells. The whole of 

 this primitive structure is covered, not only by epidermis but also 

 by the muscular layers of the body wall , both longitudinal and 

 circular. 



The bands of tissue of either side in the same segment extend 

 inwards till they meet, crossing the double nerve-chord. Fig. 34—36 n.s., 

 slightly in front of the increased number of central nerve cells which 

 marks what in other worms is the ganglionic swelling, Fig. 33, 34, 



Zool J»hr». Vli. Ahlh ( \l..r|.l, 29 



