on the Principle of Cephalization. 25 
of attachment also proceeds eee the anterior pole ao the body, 
= in all the members of the branch even t coiGaanene with 
exception of those attached by one <alvs ere g. eset 
hierdeeiiay whether it be by a byssus, confined in cells of their 
own making, or buried in the mud, it is the anterior end which 
is fixed. In several lower forms, ‘like Tridacna and An nomia, 
the point of attachment springs from the doe area, as in the 
two lowest classes. In regard to the posterior position of the 
mouth in Polyzoa and Brachiopoda, we have similar analogies 
among the Articulata ; aioe cre for example, where we have 
animals ae attached head downward, and all the ont 
arts, as in the pedunculated forms, tending toward the pos- 
terior pele: of the body; or in Li mulus, where we have such a 
decephalization, as it were, that the mouth occupies nearly a cen- 
tral position in the ve entral region. 
Again, considering the intestine as a simple tube, opening at 
each end, with the weight of structure evenly divided between 
the two openings, is it any more incredulous, that the oral open: 
ing should be a than that the anal ‘opening should be 
anterior, as in the 
In Polyzoa, the ee and anal openings occupy a similar posi- 
tion in all the forms. In Brachiopods, while the mouth remains 
in nearly a constant position, the anus terminates either in a 
median line, or by a lateral deflection of intestine to one side. 
In Tunicata, while the mouth i se a permanent position at 
the front of the sac, the anus terminates at various portions of 
the sac, generally in a a nm though there is usually a 
lateral Seite of the intestine. 
In Lamellibranchiata, nie eee and anus terminate in a me- 
dian line, with few exceptions, (e.g. Pecten) though the intes- 
tine convolutes in various ways. In Gasteropods we have again 
lateral deflection of intestine, and though in many sige the 
anus terminates in a median line, yet in the bulk of the Gaster- 
opods it terminates at one side or the other. In the Dibranchi« 
ate Cephalopods we have again the termination of the intestine 
in a median line 
he diagram ors given (fig. 1) represents an 
ideal longitudinal section of the sac, similar to 
those of Series I. The arrow within the sac 
—. the direction of rotation of the bent intes- 
e, carrying with it the heart, (see Plate, Series 
I) which i in “Brachiopoda we find on the ventral 
region; in Tunicata on the anterior dorsal re- 
gion; in Lamellibranchiata on the dorsal mon 
in Gastero on the dorsal region and — 
farther back; and in the Cephalopods at the 
posterior portion of the sac. ‘The different ciatiokg of the ~~ . 
Ant. Jour. Sc1r.—SEconD pein Vou. XLII, No, 124.—Jury, 1866. 
4 
