EMBRYOLOGY OF THE SEA BASS. 
215 
lirst furrow at points on opposite sides and a sliort distance from the poles. For the 
sake of convenience the cut Fig. 2 may be used as an illustration, tliougli it does not 
h 
Fig. 2 (from Kauber, 36). — Variation in the frog's segineii 
tation, imlt.atiug teleostcan segmentation — p., auiiiual 
pole; a. to ft., first furrow; 6. tob., second furrow; c. 
to c., cqii.atorial furrow ; 1, 2, 3, 4, fourth furrow. 
This type while unusual is not very rare. 
represent the most common type of the 
frog’s segmentation. Supposing p to be the 
upper pole of the egg, the first furrow 
and the second furrow b-h cross at points 
some distance from the pole. Wliatever be 
the precise cause which makes the fur- 
rows in the frog thus avoid the ])ole, the 
avoidance is a fact, and to it llauber has 
given the name of Polftucht. The third me- 
|l ridional cycle of furrows (the true third or 
equatorial is represented by the bounding 
line c in the figure) exhibits the same phe- 
nomenon. The individual furrows run from 
the equatorial furrow not to the pole, but 
into the several older furrows ; for instance, 
the line x may represent the course of the 
furrow in this cycle. All degrees oiPolfluoht 
may be found, and when the degree is 
great enough, and is coupled with the oc- 
currence of certain other features, the type 
of segmentation shown in Fig. 2 is produced 
Its similarity to, almost identity with, the 8-celled stage in the Teleost, can not be 
overlooked, and I think Eauber is justified in regarding the third teleostean furrow 
as homologous with the furrows 1, 2, 3, 4. This homology is further strengthened by 
the occurrence of a variation in the Teleost, which may be interpreted as a reversion, 
and as indicating that the third furrow in the fish egg was originally a true meridional 
furrow, or at least one with very little Poltiucht. Such a variation is shown in Fig, 5, 
PI. Lxxxviii (Mackerel). It is certainly very rare in the Bass and Mackerel, and the 
blastoderm figured was apparently pathological. Agassiz and Whitman record the 
occurrence of the same variation in Ctenolahrm (i, PI. cvii. Pig. 35). 
According to Eauber the first equatorial furrow of the frog lias been lost in the 
Teleost. Agassiz and Whitman would seem to believe that the a priori improbability 
of such a loss taking jilace is so great that, in spite of the variations just described, it 
is preferable to regard the first three furrows as homologous in the two groups. I do 
not see the inherent improbability of the loss. On the contrary, the disappearance of 
segmentation in the ventral half of the egg, coupled with the early contraction of the 
protoplasm (belonging to this half) towards the upper pole, make it easy, I think, to 
understand how the loss was brought about. 
II. FORMATION OF THE PERIBLAST. 
The existence of yoik nuclei in the Teleost egg (parablast nuclei, Ilis; periblast 
nuclei, Agassiz and Whitman) was discovered as long ago as 1854 (Lereboullet, 31), 
but their origin was first made out by Agassiz and Whitman in 1884 (1). These 
authors proved beyond a doubt that in Ctenolabrm the nuclei are derived from the 
marginal cells of the blastodisc, which, from the earliest stages of segmentation are 
