THE SCHIZOPODA. 



127 



tliis connection, it appears that the expectation of larvae diminished with depth, tliat of 

 adults increased with depth : the average catches per hour haul consisted 



At 25 fathoms of 93 per cent, larvse and 6 per cent, adults. 

 50 „ „ 73 „ „ „ 26 

 75 3. 5) 34 „ „ „ 65 „ „ 



100 * 20 7Q 



The next table presents the distribution of adults, of larva?, and of both taken 

 together, at various depths by " day " and " night " (as in previous cases), in average 

 catches per hour haul. It shows no evidence of a nocturnal rise of the species ; but it 

 presents some puzzling features. 



One of these is that so many more adults were caught by night than by clay at 75 and 

 100 fathoms — depths at which it is difTicult to think that the light is strong enough to 

 enable the species to see and avoid a net ; and a remarkable feature is that these large 

 night values were mainly due to three havils (34 b, c, d), all taken on one night within 

 two hours. In Euphausia Miilleri, and Nematoscelis megalops some undetermined 

 circumstances (p. 122, note) had concentrated these species at 50 fathoms at the time 

 when haul 31 b was made, but in that haul Stylocheiron Suhmil was not remarkably 

 plentiful ; in 34 b, c, d, when the latter was abundant, no such marked increase in the 

 number of the other two species was noticeable. Whatever the determining stimuli 

 may have been, it is fairly obvious that they were not the same in the two cases ; I have 

 no explanation of the facts to offer ; no entry in the log suggests a clue in the second 

 case ; but I record the observation here to show how difficult it is to get any knowledge 

 of the factors of distribution, and (incidentally) how dangerous it is to generalise from 

 isolated hauls, or from one species to another. Precisely on the same footing, the higher 

 values for larvae by day than by night are mainly due to two hauls (30 d and 30 /f), 



* Omitting 24 h, where the oomparative number of larvx and adults had been lost. 

 t The latter included also a considerable number of adults. 

 SECOND SEllIBS. — ZOOLOGY, VOL. X. 21 



