ARTIFICIAL PARTHENOGENESIS IN ANNELIDS 655 
the two- to four-cell stages, but may in exceptional cases go 
as far as the twelve- to sixteen-cell stages. We may say that 
Cheetopterus possesses a higher degree of parthenogenetic 
tendency than the Arbacia egg, which begins to segment 
later, after about twenty hours, and does not proceed beyond 
the two- to four-cell stage. 
2. The unfertilized eggs of Chetopterus are able to 
develop into swimming trochophores if they are put for about 
one hour into one of the following solutions and then put 
back into normal sea-water: 
(1) 15-20 e.c. 24m NaCl +85 c.c. sea-water 
(2) 40 2n cane-sugar +60 s 
(3) 30 23n MgCl, +70 “ 
(4) 10 5n CaCl, +90 “ 
All these solutions have one element in common, namely, 
the about equal increase of the osmotic pressure. It seems 
therefore justifiable to assume that the increase in the 
osmotic pressure or the loss of water on the part of the egg 
is the cause of the parthenogenetic development of these 
eggs. 
3. KCl or perhaps the K ions seem to possess a specific 
effect upon the eggs of Chetopterus. We shall discuss this 
fact more fully in the next section. 
Objections considered. — The possible objection that the 
eggs of Chetopterus are naturally parthenogenetic in normal 
sea-water or that spermatozoa had contaminated the sea- 
water is rendered impossible through the bebavior of the 
control eggs and the antiseptic precautions taken. As far 
as I can see, there is only one objection left, which, however, 
although far-fetched and highly improbable, shall be consid- 
ered. It might be argued that Cheetopterus is hermaphro- 
ditic, but that the eggs and spermatozoa do not mature 
simultaneously. This prevents fertilization of eggs in nor- 
mal sea-water. But the increase in the osmotic pressure of 
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