18 G Canadian Arctic Expedition, 1913-1918 



broad, and less branched; the mandibular-palp is smaller, but the maxillae 

 better developed, as also the foliaceous legs. The latter end in a long, temporary 

 swimming branch while the broader, respiratory part is as yet only developed 

 as a short lobe. There is also a distinct swelling of the last body-segments, 

 heralding the development of the genitalia; and the abdomen shows about ten, 

 indistinct segments, of which the next to the last is the narrowest, while in the 

 preceding stages the tip of abdomen is the narrowest, another adult feature. 

 The cercopods are also better "set off" from the last abdominal segment than jn 

 Sars' specimen. The general shape of the abdomen is cylindrical, it is longer 

 in proportion and more distinct from the body than in the larvae from Norway. 



The oldest ones of these (stage III) metanauplii from Colhnson point 

 showed transition forms to the next stage (IV), of which I secured a dozen 

 specimens from 2 to 4 mm. long. These have practically the same appearance 

 as Sars' fig. 17, and are described by him, p. 55. The composite eyes, foliaceous 

 legs and abdomen are better developed, the head more set off from the body, 

 but the second pair of antennae and the mandibular-palp still more reduced. 

 Labrum is still large. The oldest of them were transition-forms to the next stage 

 (V) of which I secured a dozen specimens from 4 to 6 mm. long. They corre- 

 spond fairly well with the 5 mm. long specimens figured by Sars on Tab. VI, figs. 

 5, 6, and described by him p. 55, some of my specimens belonging to this stage 

 (V) being a little younger, some of the same age, and some a little older than the 

 Norwegian specimens. 



In the oldest larvae the eleven pairs of foliaceous legs ' are well developed 

 and distinct, though none of them reach the length of the second pair of antennae. 

 The latter are now a little more than one fourth of the total length of the larva, 

 while with my stage III they are about one-third the total length. Labrum is 

 greatly reduced (less than the length of the head, while on stage II it is double 

 the length of the head) but even the 2nd maxillae well developed. The tail 

 (abdomen) is now long (about half the total length), and slender cylindrical 

 with the cercopods ^ almost lanceolate in shape, as with the adults. With other 

 words, except for the 2nd pair of antennae and the less development of the 

 genitalia these oldest larvae (stage V) are practically as the adults, and probably 

 two weeks old. In colour all these Collinson point larvae had orange-red head 

 and body (until genitalia); intestine yellow-brown with dark faeces; conspicuous 

 red-orange brown granules ^ in labrum, black-metallic eyes and the cuticula 

 white-yellow with darker mouth-parts. 



The pond in which these Branchinecta larvae occurred was a beach pond 

 at Collinson point. The larvae were not found in such parts of the pond where 

 the vegetation (grass, mosses, etc.) was prominent; but places where the side 

 and bottom of the pool was composed of mud-detritus and decaying pieces of 

 driftwood were swarming with them. Here the larvae led a true pelagic life, 

 unlike the adults (see later), keeping away both from the surface and the bottom 

 of the pond. The youngest larvae (nauplii-metanauplii) especially were very 

 active, being propelled quickly by violent strokes of the enormous second pair 

 of antennae, while the older larvae would remain more "suspended" in the 

 water, though "rowing" with their appendages. There is less than one second 

 between two succeeding strokes of the locomotory organs of the larvae, and in 

 the water they turn easily around in all directions. Particularly the youngest 

 larvae seem to be in movement all the time, the few foliaceous legs developed 

 assisting the large antennae in rowing and balancing the movements, taking 

 the larvae. off in "jumps" continually. Especially is this the case when the 

 larvae get entangled in the vegetation (green algae) of the pond; they then try 

 frantically all kinds of violent motions to get free again. This also holds for 

 the older larvae from this date, only with the difference, that the swimming 



' Swimming-branch and respiratory branch equally developed (see above). 



2 The (middle) spines in which these end are longer than with the younger stages. 



' Excretory organs? 



