In the Scotia Sea, the larvae of Thysanoessa macrura G.O. Sars, 1885 were scarce in spring (September 27 to October 6, 1971) and m a i n l y p r e s e n t at the C a l y p t o p i s I stage, while in summer (December 17, 1974 to J a n u a r y 3, 1975) they were much more abundant and much further d e v e l o p e d (up to F u r c i l i a VI) . The spawning season commences as early as S e p t e m b e r and, as i n d i c a t e d by the p r e s e n c e of numerous nauplii and m e t a n a u p l i i in summer, is rather long. T. macrura begins to spawn m u c h earlier in W e s t -W i n d -D r i f t waters than in waters of the W e d d e l l Sea. It starts to spawn s i m u l t a n e o u s l y with Euphausia f r i ~d a and E. triacantha, but s i g n i f i c a n t l y earlier than E. superba. These timings of the b r e e d i n g process are related to d i f f e r e n t i a l biog e o g r a p h i c a l c h a r a c t e r i s t i c s of these species. P l a n k t o n c o l l e c t i o n s made at depths of 500 or 1OOO m have, for g. macrura, r e v e a l e d a " d e v e l o p m e n t a l ascent" analogous to that of E. superba. O n t o g e n e t i c a l d e e p -w a t e r m i g r a t i o n s are, consequently, chara c t e r i s t i c not only for E. superba, but also for other A n t a r c t i c e u p h a u s i i d s (in p a r t i c u l a r E. frigida, but p o s s i b l y not for inshore E. crystallorophias) and, as correctly p o s t u l a t e d by several other investigators, for all oceanic e u p h a u s i i d species.