20 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



regarded as the genital sinus, is a short narrow tube of very nearly uni- 

 form diameter and shows no differentiation into the three parts described 

 by Looss in Apoblema (Hemiurus) mollissimum, viz. parts like a seminal 

 vesicle, a ductus, and a cirrus. In one specimen it was found to be par- 

 tially evaginated. The wall of this part is apparently structureless, and 

 I could not make out that it was provided with any muscle fibres. 



The genital sinus is surrounded by a cirrus-sack (sac. dr.), which also 

 encloses a very short portion of both uterus and pars prostatica. The 

 cavity of the cirrus-sack is occupied by vesicular parenchyme. 



The longitudinal muscle fibres of the body wall (Plate 3, Fig. 28, mil. Ig.) 

 in the region of the genital pore are broadened dorso-veutrally so as to 

 form vertical plates or bands. 



Female Sexual Organs. 



The ovarium is situated in the median plane about one-fourth the 

 length of the trunk from the posterior end of that part. It is broadly 

 cordate in form, with its narrow end anterior (Fig. 1, and Plate 4, Fig. 42). 

 Its transverse diameter, which averages about 0.16 mm., is greater than 

 the dorso-ventral or the antero-posterior diameters, the last averag- 

 ino- about 0.11 mm. It is thus about one-third as wide as the body. 

 The ovarium (Fig. 42) consists of a mass of ova of various sizes sur- 

 rounded by a thin homogeneous membrane, in which I could distinguish 

 no nuclei. The largest ova measure 9.6 /u, in diameter and each has a 

 very large nucleus and a small deeply staining nucleolus (Plate 3, Figs. 

 32, 33). 



The short oviduct (Plate 3, Fig. 42, o'dt.) leads backward from the 

 centre of the posterior surface of the ovarium. Its wall is somewhat 

 thicker than that of the ovary, with which it is continuous, and in it are 

 seen deeply staining nuclei. The oviduct is from one-third to one-half as 

 long as the ovarium, and just anterior to, or within, the shell-gland it is 

 joined by a duct coming from one side, the duct of the seminal receptacle. 

 This lateral duct is similar in structure to the oviduct, but shorter. 



The seminal receptacle (Plate 4, Figs. 37, 38, 42) is a spheroidal or oval 

 body situated ventral and posterior to the ovarium and at one side of the 

 median plane. The end of the duct, terminating in the seminal vesicle, 

 widens out into a flask-shaped enlargement, which has been designated by 

 Juel ('89) as the inner vesicle. Both the outer wall of the receptacle and 

 the wall of the inner vesicle show occasional nuclei, which give evidence 

 of the cellular nature of the walls. The space between the two walls 



