282 DE. G. H. FOWLEE— BISCAY AN PLANKTON: 



these clown precisely, still less can we yet deduce the ancestral form of CoiichcBcia ; but 

 they may be outlined as follow s : — The shell of the earliest larvae is very high in 

 comparison to its length, and a steady unbroken curve runs from the postero-dorsal 

 angle to the antennal recess : figure 166 shows a typical early larva. The frontal organ 

 is at first straight, unsegmented, spineless, transparent, and thin-walled ; its apex may 

 be either rounded or acute. The first antenna exhibits one bristle and four tubes, even 

 in the younger males. The inner joint of the second antenna has neither central nor 

 basal bristles. No distinction seems to be at first possible between males and females ; 

 later, the penis grows out as two rudimentary papillse, and the three bristles are 

 differentiated from the two tubes in the male antenna i. 



As development proceeds the shell becomes (as a rule) longer, but only attains the 

 adult contour gradually, through a succession of moults. The shell of the adult 

 female in the later stages tends to be fuller posteriorly than in the male (that is to say, 

 to project further behind a perpendicular dropped from the postero-dorsal angle), and 

 to have its highest point behind the middle of the length; the shell of the male, 

 speaking generally, has a straighter posterior border. The frontal organ assumes the 

 adult type, if this be highly specialised, by passing through forms which are fairly 

 constant for each stage, but are often highly difl'erent from those before and after 

 them. The frontal organ of the adult female is sometimes of a larval type {spinirostris); 

 it is rarely so highly differentiated as in the male, but this is sometimes the case 

 (haddoni) ; as a rule it is intermediate in complexity between larval and male types. 

 The principal bristle of antenna i. in the male has at first the sparse irregular minute 

 teeth which are typical of the adult female ; it does not assume the definitive secondary 

 male characters (length and armature) until the penultimate Stage II. The dorsal 

 bristle of antenna i. in the female is of comparatively late appearance (generally at 

 Stage II. or ?III.). The inner joint of antenna ii. assumes at first one or two central 

 bristles, later on it may develop basal bristles; the latter may even occur in some 

 females (haddoni). The hooks of the male antenna ii. are not developed till Stage II. 



IV. FAUNISTIC PART. 



Many reports on the various collections made by recent expeditions take for granted 

 that a specimen, merely because it was captm'ed in a closing-net, was necessarily living 

 in the zone explored by the net. This reasoning appears to me most fallacious. When 

 we remember that the abyssal benthos is almost entirely dependent for its food-supj)ly 

 upon the unceasing rain of dead organisms from the upper horizons, it becomes obvious 

 that, always and everywhere in the mid-water, there must be organisms which are dead 

 or dying and sinking to the bottom to furnish this food. Consequently, very strong 

 evidence should be forthcoming, before a species which is plentiful at or near the 

 surface is admitted to be living also in the mesoplankton of its immediate district. 

 This evidence (apart from the siiecimen being actually observed to be alive when 

 brought on board, which is very unusual in a haul at great depths) can only consist in, its 

 being captured often and in considerable numbers from the mid-water. In few cases, 



