6 Mindeskrift for J. Steenstrup. XVI. 



The anterior part of the abdomen is broad and swollen, intimately joined to 

 the hindmost thoracic segment. The whole abdomen represents three segments, but 

 these are not distinctly marked out. By far the greater part is the genital segment 

 (g); laterally this send s out a large, rounded, terminally somewhat deepened process 

 (1), ventrally it carries the two genital openings (go); the latter are close together, 

 semilunar, almost in contact with their convex sides; in front of them is often, but 

 by no means always found an unpaired rounded prominence or hunch '). The 

 posterior part of the genital segment is somewhat tapering; from a deepening in this 

 part the rest of the abdomen (representing two segments) protrudes as a short and 

 narrow appendix (ap), dorsally at its base sending out a blunt process and terminating 

 with two bifurcated claws. There is n o anus, and no trace of an intestine is 

 contained in the abdomen. 



Young females (PI. I, Figs. 5, 6, 7) difTer in general shape and several details a 

 good deal from the ripe. The smallest females found after metamorphosis are 

 0,832 — 0,912 mm in length; probably their form is essentially the same as that pos- 

 sessed immediately after emerging from the larval cuticle; but while I have found a 

 great many young males together with the cast larval skin, I never succeeded in 

 fmding with certainty the same case for the young females. The outer shape of the 

 smallest females is very nearly that of the somewhat larger, ca. 1 mm in length, 

 represented on PL I Figs. 5 — 7. ' 



The body is less clumsy than in the mature female, more cylindrical, without 

 constriction between the second and third thoracic segments; the genital segment (g) 

 is less prominent, its lateral processes (1) conical and directed backwards; all append- 

 ages are proportionally larger, the thoracic feet on second, third and often also the 

 fourth pair provided with very distinct rudiments of an inner branch (i). The 

 modifications leading to the final shape and maturity are performed simply during 

 growth, without any moultings. I have particularly directed my attention to the question 

 of moulting, but I never saw anything indicating the formation of a new cuticle 

 below the older one, and I am quite sure that after the casting of the larval envelope 

 no further moulting takes place^). 



') In one case the left side of the genital segment had behind the lateral process 1 a short, 

 sausage-shaped outgrowth. 



") The same, as far as I can see, holds good for Lernaea, Pennella^ Lernæenirus, Sarcotretes — 

 in short all members of the family Lernaeidae — ; having reached the copulatory stage (Claus, 9, 

 Tab. III, Figs. 3, 4) neither male nor female undergo any further moultings; but after copulation 

 the body of the fertilized female — especially the genital segment — grows enormously and alters 

 considerably in shape; outgrowths (f. ex. the three "horns" in Lernaea) are developed etc, while 

 the appendages — antennæ, swimming feet etc. — generally preserve the form and size of the 

 young copulatory stage. Against the general rule, therefore, part of the chitinous cuticle in these 

 cases must be subjected not only to simple expansion but also in some way or other to "growth". 



