November, 1920] 



The Canadian Field-Naturalist 



147 



Ottawa river, Hull Park, P.Q., July 6, 1919, see 

 above, (F. Johansen). 



A dozen adults (abcut 12-14 mm. some of the 

 females with eggs in broodpouch), from upper part 

 of Wilson's Creek, De Grassi Point, Lake Simcoe, 

 Ont., May 30. 1917, (E. M. Walker). 



It is greatly to be desired that additional data 

 concerning the distribution of this conspicuous and 

 interesting species should be secured from locali- 

 ties north, east and west of the present records. 



Far more common than Mancasellus tenax is the 

 other species of freshwater isopod, Asellus com- 

 munis Say. It has been known from Georgian Bay 

 and Toronto, Ont., and in the United States from 

 Massachusetts to Michigan. It will be seen from 

 the new records given below that it has a much 

 wider distributicn in Canada than formerly known, 

 though we have no definite records of it from the 

 Maritime* and the western provinces. Nothing is 

 Icnown about its northern limit on this continent, ex- 

 cept that it is very common around Ottawa, both 

 on the Ontario and Quebec side. Its distribution 

 is prcbably very much the same as that of H^alella 

 f(mcf(erbocl(eri, which means that it may occur in 

 scuthern Alaska, but that it probably does not ap- 

 proach the barren grounds of this continentf. To 

 a still larger extent than Hyalella, and in the same 

 way as Mancasellus it appears to be a woodland 

 species, and is therefore perhaps not found on the 

 plains of the Canadian west. Where it occurs it 

 IS very common, and is found in great numbers both 

 in rivers and large lakes and also in ponds and tem- 

 porary pools and streams, both on clean bottom and 

 also among much vegetation, dead leaves, etc. 



In northern Europe this genus is represented by a 

 clcsely allied species the well-known Asellus 

 aquaiicus Linn., which has been recorded by Pack- 

 ard from Labrador and may occur in Newfound- 

 land. Not much has been recorded hitherto regard- 

 ing the development (life-history) of Asellus com- 

 munis. I am, therefore, glad to be able to add some 

 original observations which I have made recently 

 during my collecting trips to various localities in 

 Canada. On April 20, 1919, I collected in a 

 pool stream in swamp at Deschenes, P.Q., near 

 Ottawa, some females, 1 cm. long, which had many 

 white eggs in the broodpouch, J as well as some 

 males, 1 '/2 cm. long. These Crustacea were placed 

 in a jar for rearing, and two weeks later young 

 ones that emerged were noticed. These latter were 

 carried in the broodpouch of the mother-animal as 

 late as May 6, (until the end of May in 1920), 



•See iultliiiDiial n(it<'s. 



+ 1 fouml neither il nor Mancusellus alonj;- the 

 arctic coast of Alasl^a and western Canada. 



tin 1920 the females first carried eggs in the be- 

 ginnini; of May. 



moving freely around inside their cage, and when 

 the mother-animal was touched some of the young 

 ones would emerge and swim or crawl around.** 

 These new born Asellus communis are from 1 to 

 1 !/2 mm. long; they have practically the appear- 

 ance of their parents (well-developed appendages, 

 etc.), though the head is rounded and of the sam-. 

 width as the succeeding segments and the terminal 

 plate (telson) correspondingly large. In color they 

 were pale white, with dark eyes and the brownish 

 intestinal canal and pale-pink "gills" (abdominal 

 feet) shining through the cuticula. While sinking 

 to the bottom or crawling over the latter the an- 

 tennae, legs and "gills" move continuously, each 

 kind of appendage performing its particular func- 

 tion (feeling, crawling, respiration). I kept these 

 young isopods for several months and could easilv 

 have kept them longer, if I had had time to con- 

 tinue my observations. The energy with which 

 they crawled around looking for food or sought to 

 escape when I tried to catch them was certainly 

 wonderful, all the appendages going in one whirl 

 and the body twisting as well. When about a 

 month old they were not much larger (about 2 mm.) 

 than when first born; they were now becoming 

 brownish. I preserved samples of them (June 

 2). It will thus be seen, that the first brood of the 

 summer is born in the beginning of May (near 

 Ottawa), and that their growth is rather slow. It 

 is interesting to note that even egg (brood) -carrying 

 females of this species are considerably shorter than 

 the males (maximum size of females noticed 1 cm.), 

 sometimes even only half the size (8 mm.), of the 

 maximum size of the latter ones. Females secured 

 at Gatineau Point, P.Q., near Ottawa on June 

 14, 1919, had the brood pouches empty; on the 

 other hand females secured on July 6, 1919, in Hull 

 Park, P.Q., had the eggs (second summer-brood) 

 in the brood pouch. The same day (July 6) and 

 place I secured also as has already been mentioned 

 a 3 mm. long young Asellus communis, probably 

 of the first summer-brcod and now about two 

 months old. It had already the grayish dorsal 

 color of the full grown females (the color of the lat- 

 ter ones is less "spotted" and brown than that of the 

 males), and could thus by its color alone be easily 

 distinguished from the young Mancasellus of a cor- 

 responding (1 mm. larger) size also found on this 

 date. Other female Asellus communis secured at 

 Alexandria Bay. Thousand Islands, N.Y.. on Sep- 

 tember 1st, 1919, had also eggs in the brood pouch, 

 thus carrying what would probably be the third 

 brood of the summer. Females from a pool near a 

 quarry cutside of Hull city, P.Q., collected on 



**I have observed the same in the case of Mesi- 

 dotlie.a entomon in ilie arctic. 



