316 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.39. 



In the Caligidse while the ovary is situated in the cephalothorax 

 the eggs formed there are very small, simple nucleated cells, entirely 

 without yolk. In this condition they pass down into the genital 

 segment, which is much enlarged during the breeding season, and in 

 which the posterior portion of the oviduct (uterus) is also enlarged 

 and strongly convoluted. Here the eggs remain some time, increas- 

 ing in size by the acquisition of yolk particles, and becoming strongly 

 flattened or biscuit shaped in a single row along the terminal portion 

 of the oviduct. But the part of the duct just inside the external 

 opening is so convoluted that quite a little of it lies in the same 

 straight line with the axis of the external sack. Thus the eggs, 

 already flattened, pass out through the os uteri and are pushed 

 straight back along the axis of the external tube. The only change 

 is an increase in width and a corresponding decrease in thickness as 

 they emerge into the external tube. 



Here in the Ergasilidse the conditions are very difl'erent. The 

 ovaries are situated in the cephalothorax as before, but the eggs are 

 fully formed there, taking on the yolk particles and attaining their 

 maximum size. They then })ush back through the oviduct one by 

 one, being compressed a little laterally, but not flattened into a 

 biscuit shape. They pass through the genital segment as rapidly as 

 through any other portion of the oviduct, and are at once extruded 

 into the external sack. The opening of the oviduct, however, is on 

 the side or dorsal surface of the genital segment and not at its pos- 

 terior end. Hence the terminal portion of the oviduct inside this 

 opening does not point backward in the direction of the body axis, 

 but outward, more or less at right angles to that axis. But the 

 external sack as soon as it acquires any length at all is carried back 

 alongside the body and approximately parallel to the body axis. 

 Hence the issuing eggs, instead of being passed out along a contin- 

 uous straight line, have to turn almost at right angles as soon as 

 they get into the sacks. This prevents them from forming in a 

 single straight row and produces a multiseriate arrangement, similar 

 to that found in Cyclops and other free-swimmers. 



The eggs mature in the posterior portion of the ovaries individu- 

 ally or in small groups and not collectively, and pass out through the 

 oviduct similarly. Nordmann, in his admirable account, says: 



Die Beobachtung Ramdohrs, dass die Eierstocke ihren Inhalt nicht auf einmal in 

 die Trauben ausleeren, stimmt mit meiner hieriiber gemachten Erfahrung in sofem 

 tiberein, als auch bei Ergasilus, wiihrend die Trauben schon mit Eiern augefiillt sind, 

 zugleich noch in den Eierstocken minder entwickelte Eiergruppen wahrgenommen 

 werden (p. 12). 



Each of these "Eiergruppen" contains but two or three eggs, 

 sometimes only one, and as there is quite an interval between the 

 ripening of successive groups, the external egg-sacks fill out slowly. 



