342 ME. E. E. UNWIN: NOTES UPON THE 



•remain for soma days in the brood-pouch, eating the debris and generally- 

 getting used to life before struggling out of the pouch at the hinder end. 

 There is no general escape of the young ; they push out by twos and threes, 

 and even after a week or ten days one or two young Aselli can be found in 

 the pouch. 



Here are three typical periods of development : — 



Eggs laid Feb. 18th ; young escaping Mar. 20th. 

 „ Mar. 7th ; „ „ Apr. 7th. 



„ Mar. 28th ; „ „ May 1st. 



Soon after the escape of the young, the female passes through another 

 ccdysis and returns to the condition similar to that of the normal female. 

 The large oostegites are replaced by small processes. 



Note upon a variation of the 1st pleopod of the female. — In PI. 25. fig. 9 is 

 shown a curious variation of the 1st abdominal appendage. The normal one 

 is seen in PI. 25. fig. 8. It approximates to the 2nd abdominal appendage 

 of the male (PI. 25. fig. 7). I discovered it whilst watching the circulation 

 of blood in the oostegites of a living female with eggs. The unusual 

 appearance of the appendage attracted my attention. I examined at once 

 every available female, 35 in number, but did not find another with any 

 such variation. Ernest Ewaet Unwin. 



Bibliography. 



Kaulbersz, G. J. — " Biol. Beobach. an Asellus aquaticus." Zool. Jahrb., 



Jena (Abt. f. allg. Zool.), 1913, Bd. 33. 

 KiMUS, J. — " Recherches sur les Branchies des Crustaces." La Cellule, 



t. xv. 2 e fasc. 

 Leydig, F. — "Uber Amphipoden und Isopoden." Zeitschr. f. wiss. Zool. 



xxx. Bd. Suppl. 1878. 

 Rosenstadt, B. — •" Organ, von Asellus aquaticus.'" Biol. Centralbl. viii. 



1888-9. 

 Sars, G. 0. — Histoire naturelle des Crustaces d'eau douce de Norvege. 



1807, pp. 93-123. 

 Schneider, R. — "Eiu bleicher Asellus in d. Gruben v. Freiberg im Erzge- 



birge." Sitzb. Kgl. Pr. Akad. Wiss. Math. u. naturwiss. Mitth. 



Berl. 1887. 

 Wege, W. — " Morpb. u. Exp. Studieu. Asellus aquaticus.''' Zool. Jahrb. 



(Abt. f. allg. Zool.), xxx. 1911. 



