956 MR. H. R. MEHRA ON TWO NEW INDIAN 



What oorresponds to the a.trium in other forms is a long 

 tubular structure consisting of three parts. The first part, that 

 into which the vas deferens opens, is a dilated chamber, ovoid in 

 form, to which I restrict the term atrium ; and the i"est of the 

 tube I call the atrial duct. This is much convoluted and enclosed 

 in a thick sheath of muscle fibres which form a chamber — 

 the coelomic or muscular sac. The atrium has its long axis 

 parallel to that of the body (PI. I. fig. 3, text-fig. 4 ; and 

 PI. II. figs. 5, 6, & 7) ; in a fully mature form it is about 

 143 fi in height, 92-114 /.t in breadth and 192 jj. or about 

 i- mm. in length ; in the posterior portion however, its height 

 is only about 74 ju. Its wall consists of a muscular sheath of 

 5-7 yit thickness, which is surrounded externally by a thin layer 

 of peritoneum ; and of the inner epithelium, which in many of 

 the specimens approaching advanced sexual maturity loses its 

 cellular character, appears simply frothy and stains like the 

 coagulum with which the atrial cavity is filled. Though the cells 

 have lost their structural features and nuclei, it can be recognized 

 that they have increased in size. The cells lining the hindermost 

 part of the atrium retain, however, their columnar outlines and 

 their nuclei. The secretion of the larger, anterior portion of the 

 atrium appears to be similar to that of the prostate cells. 



Prostate. — The prostate gland is characteristic of the Tubificidae 

 among the Microdrili. 



Connected with the atrium on its ventral side nearer its 

 rounded anterior end there lies a voluminous mass of gland cells, 

 which surrounds it, and a greater portion of the vas deferens in 

 front; it has the form of an irregularly shaped lobate mass, some- 

 times reaching as far back as the coelomic sac. The mass lies 

 dorsally to the ovary, which occupies a ventral position in this 

 region of the body (PI. I. fig. 3). The cells are large and 

 pear-shaped with the nuclei contained in the outer swollen 

 portion ; their narrow inner portions or fine ductules lie near 

 the centre of the gland (PI. II. fig. 5) snd converge towards 

 the point where the prostate is in communication with the 

 atrium, while the broad outer portions of the cells lie towards 

 the periphery. When the prostate is fairly well developed, 

 which was the case in most of the specimens under examination, 

 the ductules or the inner portions of the cells lose their entity 

 and become more or less disorganized ; and in the period of more 

 advanced maturity, the outer portions of the cells become more or 

 less dissolved, and the cellular structure disappears, only a few 

 nuclei being left here and there. As the cells lose more and 

 more in structure, the secretion becomes collected in a mass 

 and passes straight into the atrium, where the prostate is 

 connected with it (PI. II. figs. 6 & 7). The prostate com- 

 municates with the atrium by an opening 42 /a wide ; here 

 both the muscular and epithelial layers of the atrial wall are 

 absent, so that the prostate appears to arise as an outgrowth 

 of the atrial epithelium. In the mature worm the atrial 



