studies on murine Ostracods 139 



f u r c a 1 lamella has seven claws, which decrease fairly unifonnly in length and strength 

 the more proximally they are situated. 



Stage IV: — ^Shell: Average length, 1,2 mm. In the third larval stage the bristles on 

 the surface of the shell are somewhat fewer than in the first and second stages; this decrease is still 

 more striking in this stage, the surface of the shell being almost smooth. The sixth limb is 

 represented by a rounded, unjointed or almost un jointed, two-lobed plate; cf. fig. 20 of this species 

 in the special part of this work; the proximal lobe is only furnished with one bristle, the distal one 

 has no bristles, armed only with long, stiff hairs. The seventhlimb is also found; it is repre- 

 sented, however, only by a small, imdifierentiated process pointing upwards. Each furcal lamella 

 has six claws, which decrease fairly uniformly in length the more proximally they are situated. 



Stage V: — Shell: Average length, 1 mm. Even in this stage the shell has about the 

 same shape as that of the mature female. The dorsal margin is, however, somewhat more imiformly 

 rounded. The sixth 1 i m b is less flattened and is simple, peg-like, without bristles, furnished 

 only with stiff hairs. The cleaning limb is quite absent. The anterior limbs are 

 also of a decidedly larval type, with a very much reduced number of bristles, but yet of about the 

 definitive type. Each furcal lamella is armed with from three to five claws, of which 

 the two distal ones dominate very decidedly over the others in size and strength; the proximal 

 ones are very weak, spine-like; cf. fig. 21 of this species in the special part. The rod- 

 shaped organ and median eye are well developed as in the preceding stages, but 

 have a very pronounced embryonal character. 



This was the youngest freely living stage I found. 



Stage VI: — This is hypothetical, as no specimens have been found so far. 

 The average length of the shell, as calculated theoretically, = 0,83 mm. 



Stage VII: — This is still in the brood chamber of the mother. Shell: Average 

 length, 0,7 mm. It is oval; the rostral incisur is broad and rather shallow. The sixth 

 and seventh limbs are absent. The other limbs are developed with about the 

 definitive type; the posterior ones have, however, rather few bristles. 



Measurements: — 



142 specimens of this species from the above-mentioned station were measured. The measure- 

 ments of the lengths of the shells gave the following result as shown graphically, fig. XXI. 



It foUows from this figure that the specimens investigated could be divided intt) six 

 distinct classes of length. In each class the length differs by about three divisions. The 

 class 80 — 82 consists of mature females (there were no mature males in this sample), the others 

 consisted of larvae. I succeeded in distinguishing males and females only in the two oldest 

 larval stages, as is shown above; both sexes appeared to have the same length of shell. Thus 

 classes 54 — 56 and 68 — 70 include both males and females. 



The g r o w t h - f a c t o r as determined empirically was 1,23, 



^\^ith this growth- factor the following average lengths are to be expected theoretically: 

 Stage V Staae IX Stage III Stage II Stage I Mature individuals. 



29 d 36 d 44 d 54 d 66 d 81 d 



28— 30d 34—36(1 43 — 4r) d 54— 56 d 68— 70 d 80— 82 d. Actiuil lengths. 



