38 PATTEN. [Vou. XII. 
Dohrn and Osborn to that effect. But that they are not 
nauplii is obvious because they are mere fragments of embryos, 
minus brain, oesophagus, and one or more of the anterior 
thoracic segments. One cannot always determine with cer- 
tainty just what appendages are preserved in these false 
nauplii, but in most cases they appear to be the three posterior 
pairs of thoracic appendages. 
There are three reasons in favor of this view: (1) In some 
cases that clearly belong to this category, the cephalic lobes 
and the two or three following segments are quite rudimentary, 
showing marked anterior degeneration, while the three pos- 
terior appendages are of fair size. In Fig. 25 is a typical case. 
Here the cephalic lobes are reduced to a rounded plate of cells 
with the remnant of the oesophagus in the centre, and they 
are separated from the thorax by a wide space along which no 
organs are developed. 
(2) In cases where there has been anterior degeneration, 
accompanied by the fusion of right and left halves, the last 
three pairs of appendages (known to be such by the presence 
of the flabellum on the sixth) undergo the least modification or 
degeneration, and persist long after every organ in front of them 
has disappeared. Figs. 44, 48, also 94, 96, 97, 102-104. 
(3) When transverse fission occurs, it divides the embryo 
between the third and fourth pairs of thoracic appendages into 
two parts; the posterior one usually persists for a long time 
after the first part has disappeared, showing that it has the 
greatest vitality. Figs. 51, 98, 103. 
It is: therefore very probable thatin Pigs. 25,26, 27,-33.734, 
35, 62, 65, 66 the segments present are the 4th, 5th, and 6th 
thoracic. But it must be observed that in Figs. 31 and 32 the 
second and third pairs of appendages are much better developed 
than the posterior ones. And also in Fig. 27 the rudiments of 
the oesophagus and cephalic lobes lie directly in front of the 
first pair of appendages. The same position of the cephalic 
lobes and oesophagus is observed in Figs: 33,.34, 45, 62,05, 
66,67. It is thus obvious that entire segments may be omitted 
without leaving any apparent break in the series. This is 
especially clear in Fig. 27, where three thoracic segments are 
