Isopoda 21d 



Station 306. Demarcation point, Alaska, 3 fms.; mud and stones, no vege- 

 tation (on bait-trap); May 9, 1914. 1 adult specimen., 



Station 316. Basin in outlet from big lake at Konganevik (Camden bay)^ 

 Alaska, from fresh water; June 30, 1914. 3 adult females and about 50 young 

 specimens. 



Mr. Johansen states: 



"Followed up the outlet from the big lake inland, from the sea-beach. The 

 course of this small creek is much winding; especially where it (nearer the sea) 

 flows between low tundrabanks. In its upper part it can be rather easily 

 waded, as it here flows through swampy tundra; while in its lower part it forms 

 deep holes or basins with big boulders on the bottom, covered with vegetable 

 detritus, moss, grass, etc. In the quite fresh water of these basins I saw several 

 of the common, littoral-marine Idothea crawling between and over the boulders; 

 and I caught three of them (all fullgrown; eggs and new-born young ones in 

 brood-pouch). The animals probably have succeeded in getting into these 

 basins at high tide through the lagoons forming the beach-end of the outlet; 

 and they have then remained in the quiet waterholes for the purpose of feeding 

 among the vegetation here, and maybe also to bring forth their young ones 

 here. They were not found in the upper part of the outlet." 



Station iOg. Bernard harbour. Northwest Territory, June 20, 1915, from 

 stomach of a female Cristivomer namaycush. 2 adult specimens (mutilated). 



Station 41r. Bay East of Bernard harbour, Northwest Territories ; in 

 burrows in sand on littoral region; August 14, 1915; 12 young specimens. 



Mr. Johansen gives the following interesting description of the habits of 

 M. entomon: 



" Examined the intertidal zone along the beach of the bay. The littoral 

 region here is made up of extensive sand-flats with scattered boulders; and at 

 low tide many shallow water-pools are left. In the sand-bottom were many 

 winding tracks like those Lepidurus glacialis makes in the mud-bottom of lakes 

 made, as I found by a small (ca. 5-20 mm. long) Idothea sp. buried at the one 

 end of the track and leading it further from here. Some of the tracks were in 

 sand not covered by water now (low tide) ; and besides being able to feed con- 

 tinuously the animals are hidden and protected (from enemies and the sun) in 

 these burrows, until the high tide comes back. I observed that the animals 

 make these burrows, by first sticking their head-end into the sand; and then the 

 particles of this below the anima-l are carried backwards by quick, violent and 

 continuous movements of the foremost, abdominal legs (in much the same way 

 as a sand-burrowing wasp). The making of the burrow-track is thus effected, 

 in a similar way as with Lepidurus glacialis (foliaceous legs); while the free- 

 swimming in the water of these Idothea (probably all younger stages of the 

 common I. entomon) is effected by the long body-(walking)-legs (see October 14, 

 1913). The colour of these young Idothea (found today) is as follows: Uniformly 

 cuticula-brown with black eyes and pigment (dark brown) dorsally (strongest 

 on forepart of head, along middle-dorsal and as a cross-band just in front of 

 the telson). While these young Idothea thus are common at the beach around 

 here, I have only found very few of the fullgrown ones, living here (compare 

 the extremely common occurrence of the latter ones in the littoral region of the 

 Alaskan Arctic Coast). 



"The life-history cycle of this Idothea is thus: 



" 1) Embryo-development and the newborn young ones in the mothers' bj ood- 



pouch (June 30, 1914). 



"2) The just 'emerged' young ones are pelagic, swimming in the water in the 



late summer and fall (September-October, 1913). 



