468 MEAD. Vor, Ix, 
The history of the prototroch in Clymenella is similar in 
every detail to that of Amphitrite. 
The paratroch in Amphitrite consists of four cells, one of 
which is the descendant of x', the other three of 47. They are 
differentiated some time after the completion of the proto- 
troch. The cells) at first! le im the are of @ circle! at. the 
posterior lip of the blastopore, two on either side of the middle 
line (Fig. II). Two of them may be called dorsal, and two 
ventral, paratrochal cells. The dorsal ones unite in the median 
line. The ventral ones, on the contrary, are widely separated 
at first, and are later brought together by the general lateral 
movement and concrescence to be described below. 
Within the arc are small cells which later give rise to the 
proctodaeum —‘terminal cells. The paratroch persists until 
the larva has attained five or six setigerous segments. 
Mucous Glands. — The apical cross in Amphitrite is so 
exactly similar to that of Nereis that no description is neces- 
sary. The cells, c'5 and d*5, which in Nereis become the 
‘head kidneys,” in Amphitrite give rise to a pair of huge 
mucous glands. Other mucous glands occur. 
AXIAL RELATIONS. 
In Amphitrite, in the four-celled stage, a vertical plane 
passed through the middle of the cells 4 and D, corresponds 
= to the sagittal plane of the future 
: animal (Fig. I). 
The apical pole, indicated by 
the position of the polar bodies, 
corresponds to the future anterior 
end, the future posterior end being 
near the opposite (vegetative) pole. 
The cells A and C represent, then, 
the right and left quadrants of the 
early trochophore; & the ventral, and D the dorsal quadrants, 
respectively. But in the elongated trochophore the descendants 
of the cell Y come to occupy not only the whole dorsal region 
of the body, but at the posterior end, the lateral and ventral 
regions as well. 
Tight 
