264 DR M'INTOSH ON SOME POINTS IN THE STRUCTURE OF TUBIFEX. 



so many curves and spirals that it is impossible to unravel them, (vide Plate 

 IX. fig. 16), until a more favourable condition of extension ensues. It is a fact 

 of interest, that while the vascular distribution is more apparent in this species, 

 the perivisceral corpuscles are less developed. 



Generative Organs. — The first swollen segmental organ in the shorter form 

 (Tubifex rivulorum), as M. Clapakede observes, occurs in the eighth segment. 

 In one specimen the dilated portion of tjbie organ was at the anterior border, 

 and on the same side the coils of the duct had entered the seventh; while on 

 the other side neither coils nor dilated portions were visible in either seventh 

 or eighth segments, but both were present on that side in the ninth. Consider- 

 able room, therefore, exists for misunderstandings. The segmental organs 

 (Plate IX, fig. 18, from behind the middle region,) vary a little in shape, and 

 some in developed specimens are tinted brownish by transmitted light. The 

 shorter tube (a) is attached to the septum in front, opening through the mem- 

 brane by a slightly dilated and ciliated opening. The long coil, again, opens 

 externally, also by a very slightly enlarged extremity, at a point a little posterior 

 to the former, but in the same segment. 



The sexual pore lies a short way behind the ventral bristles of the eleventh 

 segment, and has the form of a conical papilla (Plate X. fig. 10), which is per- 

 forated at the summit. Occasionally spermatozoa are observed to issue from 

 the tip. In this instance the copulating organ is slightly protruded. 



The integuments, as already noted, from the tenth to the fifteenth segment 

 become at the reproductive season very opaque, and hence the difficulty in 

 making an accurate description is much increased. The tenth and eleventh 

 segments especially swell out, and become opaque white at the period of 

 perfection. 



Male Organs. — In those with undeveloped (or only slightly developed) 

 generative organs the testicles are found at the anterior border of the tenth 

 segment, and the segmental organ in the eleventh is small, showing that it only 

 becomes enlarged with the other structures subsequently. Under the same 

 circumstances coils of the ciliated duct of the segmental organ are found at the 

 posterior border of the twelfth segment. At a further stage of development 

 the testicles form large opaque-whitish masses, which are at first granular 

 (Plate X. fig. 19). What appears to be a further stage is shown in fig. 20, 

 Plate IX., the cells being filled with a vast number of awl-shaped bodies, 

 measuring l2 1 50 of an inch long, rounded at one end, and having a slender style 

 at the other. There are also numerous minute ovoid granules in the cell, their 

 long diameter ranging from b J- 6 o to 6 J 0o of an inch. The bodies represented 

 in fig. 6, b, c, d, Plate IX., are probably also stages in the development of these 

 structures. 



In their fully developed state the spermatozoa resemble wavy or zig-zag 



