SALPA LIFE-HISTORY 



107 



which are for a time masked by the phenomenal activity of 

 certain cells of extraneous origin, the "kalymmocytes," derived 

 from the follicular epithelium surrounding the ovum. These 

 follicular kalymmocytes migrate into the ovum, surround groups 

 of blastomeres, and arrange themselves so as to reproduce the 

 essential structure of the future embryo for which they form 

 what may be termed a scaffolding or temporary support. After 

 a time the blastomeres become active, proliferate rapidly, and 

 finally press upon and absorb the kalymmocytes, and so eventu- 

 ally take their proper place in building up the organs. Some 

 observers .regard the kalymmocytes as being passive and nutritive 

 only in function. 



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Fig. 67. — Young solitary 

 Salpa democratica-viucro- 

 nata attached to the 

 parent by the placenta. 

 atr.ap, Atrial aperture ; 

 ir, dorsal lamina ; cil.gi\ 

 dorsal tubercle; ebl, 

 elaeoblast ; end^ endo- 

 style ; n.gn, nerve-gang- 

 lion ; oes, oesophagus ; 

 or.ap, branchial aperture ; 

 peric. pericardium ; pi, 

 placenta ; red, intestine ; 

 stol, stolon ; stom, stomach. 

 (From Parker and Has- 

 well, after Salensky.) 



At an early period in the development a part of the surface 

 of the embryo, on its ventral edge, becomes separated off, along 

 with a part of the wall of the cavity (" oviduct " — a diverticulum 

 from the atrium) in which it lies, to form the " placenta " (Fig. 

 67, pi) in which the einbryonic and maternal blood-streams 

 circulate in close proximity, and so allow of the conveyance of 

 nutriment to the developing embryo by means of large migrating 

 placental cells. At a somewhat later stage a number of cells 

 placed at the posterior end of the body alongside the future 

 nucleus become filled up with oil-globules to form a mass of 

 nutrient material — the "elaeoblast" (Kg. 67, ell) — which is 

 used up later in the development. Many suggestions have 

 been made as to the homology and meaning of the elaeoblast ; 

 but it may now be regarded as most probable that it is reserve 

 food-material associated with the disappearing rudiment of the 



