DR M'INTOSH ON SOME POINTS IN THE STRUCTURE OF TUBIFEX. 265 



lines (Plate IX. fig. 21), sometimes with attached globules or loops resembling 

 heads, but more frequently without them. They do not swim actively about 

 on escaping through a wound, but spread themselves insensibly over the field 

 of the microscope. They often, as M. d'Udekem shows, surround a sperm- 

 cell so completely as to resemble a seed with its downy pappus. 



The first testicle, in those with developed organs, occupies to a greater 

 or less degree one side of the ninth segment; and occasionally it is little 

 developed while the second stretches to the sixteenth segment. I have also 

 seen the first testicle slip entirely out of the ninth segment, and lie towards 

 the posterior part of the tenth. It is attached to the septum between the 

 ninth and tenth segments, in the angle next the intestine (in ordinary views, 

 c, fig. 6, Plate X.) In a large specimen there was the unusual appearance of a 

 glandular organ resembling a testis with sperm-cells in the fifth segment, and 

 the seventh and eighth had each two of a similar nature. The ninth had the 

 vas deferens with its trumpet-shaped aperture fixed in the septum between it 

 and the eighth. The developed organ (testis), moreover, stretched from the 

 bulged septum last-mentioned to the fifteenth segment. The ordinary condition, 

 however, is that the first testis occurs in the ninth segment, the receptacles in 

 the tenth, the ovaries in the eleventh, and the second testis in the twelfth 

 segment. 



The eleventh segment also holds the large coils of the vas deferens (Plate 

 X. fig. 6, b), which, moreover, often slip into the twelfth. The trumpet-shaped 

 aperture is connected with the septum between the tenth and eleventh segments. 

 It (vas deferens) is clearly a development of an ordinary segmental organ, as 

 indeed most authors state. 



In the sixteenth segment of one example there was a large parasite (Plate X. 

 fig. 11) in the lobule of the testis, and extending throughout the entire length 

 of the division. Its interior was filled with cellulo-granular matter, and in 

 contraction its sides were distinctly crenated, while the body was crossed by 

 transverse rugae, like a larval cestode. There is a short median furrow passing 

 from a notch in its anterior or smaller end. It is not ciliated. 



Female Organs.- — In the early condition the ovaries are observed at the 

 anterior border of the eleventh segment, attached on each side to the septum, 

 close to the dorsal vessel and intestine (Plate X. fig. 12, a, b). In this state 

 they are composed of granular cells. The developed organs (sometimes of an 

 orange colour) stretch to the fourteenth, fifteenth, and subsequent segments, 

 and when compressed give exit to a vast mass of fatty granules. 



The seminal receptacles (Plate X. fig. 6, a) are amongst the most distinctly 

 marked organs in the developed animal, and are at once distinguished by the 

 lively contractions which ensue when they are filled with spermatozoa. They 

 occupy nearly the whole of the tenth segment, and the apertures have the form 



VOL. XXVI. PART II. 3 Z 



