542 Ake nordenstam 



Variation in form of body and month-parts. 



The form of the body is slightly different in males and females. The males 

 (PI. 20, fig. 7) have the anterior and posterior part of the thorax a little broader 

 and the lateral thoracic margins less convex than the females. This cannot be 

 very clearly seen in the males when they are full of food (PI. 20, fig. 9), and 

 consequently the coxal plates in this case (cf. below) protrude very distinctly in 

 the dorsal view. 



The form of the body is also different in adult and immature specimens. 

 The latter are short and broad, as shown in PI. 10, fig. 7. Adult individuals 

 (PI. 20, fig. 8) are longer and relatively narrower, owing to a considerably 

 greater length of the visible part of especially the last three thoracic segments. 



The specimens are still more extended when they are very full of food 

 (PI. 20, fig. 9). In such cases the ventral side is extremely swollen up to the 

 1st thoracic segment (PI. 20, fig. 10). The 3rd to the last thoracic segments 

 are visible in their whole length, and consequently, seen from above, still 

 longer than usual. The coxal plates on the 3rd, 4th and 5th segments pro- 

 trude more in the dorsal view and are well separated from each other. Of 

 the abdominal segments only the ist is for the most part hidden, but can be 

 seen laterally. 



A difference between adult and immature specimens is also to be seen 

 in some of the mouth-parts, i.e. the first maxillae, which in immature specimens 

 have their second joints on the outer lobes very short (fig. 9e); these joints 

 are considerably longer and stronger in adult males (fig. 9 c). 



In the females with marsupium all mouth-parts except the mandibles are. 

 altered. The ist maxillae (fig. 9 d) have their 2nd joints of outer lobes short 

 and resembling those in the young individuals. The 2nd maxillae (fig. 9 h) are 

 broader than in other individuals and like the maxillipeds (fig. 10 b) furnished 

 with ciliated setae. Perhaps they may be able to assist these mouth-parts, in 

 a sHght degree, in their special function in fertile females. The 3rd joint is 

 broader than in other individuals and its apical setae are broad and very short. 

 The maxillipeds (fig. 10 b) are altered in the usual way. 



There are also other variations in mouth-parts, but I could not be quite 

 sure whether these variations are due to sex only or also to age. In the 

 mandibles (fig. 9 a and b) the molar is often furnished with small teeth-like 

 setae in the male (fig. 9 a), or more slender setae in females with marsupium. 

 The inner lobes of the first maxillae generally have knob-like ends. In im- 

 mature specimens they are, however, cylindrical throughout. This is the case 

 also in one specimen (female with marsupium.? (fig. 9 f)), which also differs in 

 having its 2nd joint of outer lobe provided with two parallell rows of teeth. 



Description. 



Body generally extremely hairy and much more so in adult individuals 

 than in immature specimens. Generally, in adult specimens, the whole body 

 is covered with hairs, and there are also sparse setae on the head. Often the 

 head and sometimes the ist and 2nd segments are free from hairs. 



Small immature specimens (about 3 mm) are almost without hairs and 



