618 ME. A. D. MICHAEL ON THE 



the tuuica propria, have a tendency to be columnar, but the deeper layers are more 

 round, the innermost being often more or less comma-shaped, with swollen ends, which 

 project into the lumen. The eggs lie some time in the oviduct, and develop greatly 

 there : yolk-division commences, and proceeds to a considerable extent, before the ova 

 pass into the duct ; but it is completed there, and. the egg increases in size greatly while 

 there ; it is in this organ also that it receives the strong chitinous covering with which 

 it is provided before it leaves the body of the female. The thick walls of the duct are 

 manifestly secretory ; in joung females, before yolk-division has commenced, the lumen 

 of the duct is generally full of a granular secretion, which probably is a nourishing fluid ; 

 it is found in more mature specimens, but then the ova so fill the duct as to allow but 

 little room for other things. 



The Receptaculmn semlnis, or spermatheca (figs. 25, 43, rs), is an azygous sac formed by 

 an in-pushing of the wall of the oviduct not far from the external labia, but still not in 

 the flexible membranous portion of the duct which adjoins the labia; it is but slightly 

 seen in immature females, and sometimes not at all in very old. ones after the eggs are 

 all, or almost all, impregnated ; in females which have arrived at maturity only a short 

 time but have been impregnated, this sac is crowded with spermatozoa. It is not hard 

 or chitinized, but is a soft and flexible organ with its walls composed of rather columnar 

 cells, and its exterior in most parts covered by a layer of fine constrictor muscles. 



The External Labia do not difi"er from those of the male, except in being somewhat 

 larger and rather more spongy in construction. 



The Respiratory Organs. (Fig. 45.) 



These organs have a general resemblance to the corresj)onding parts in Trombidimu, 

 which have been admirably and correctly figured and described by Henkin (6. fig. 7) ; 

 but they vary considerably from that type; they are almost similar in the different 

 species of Bdella which I have examined, any small points in which they do not agree 

 will be noticed. 



In Bdella Basteri there is, on each side of the body, a long tubular air-chamber 

 (fig. 45, ac) which has an almost even diameter, usually of about -05 mm. throughout. 

 This air-chamber commences immediately behind the mandible, and continues backward 

 in a course which typically should be almost straight, but which generally becomes 

 slightly tindulating from the pressure of other organs, until it reaches the genital organs ; 

 it even passes among these, usually penetrating between the two arms of the great 

 mucous gland of the male, and between the ovary and the alimentary canal of the female. 

 It ends blindly both anteriorly and posteriorly ; both ends are rounded. The anterior 

 end is attached by a double tendinous ligament {tl) to a fold of the cuticle close to the 

 lower posterior corner of the mandible. At a distance from the anterior end of the air- 

 chamber eqvial to abovit two-thirds of the length of the air-chamber itself, there springs 

 from the dorsal side of the chamber a main tracheal trunk {tra), about one-third or one- 

 quarter the diameter of the air-chamber ; it turns sharply forward inmiediately and runs 

 parallel to the anterior part of the air-chamber the whole length of that organ. In the 

 drawing the two are slightly separated in order to show them distinctly, but in nature, when 



