Morse.] Sat [March 19, 
accordance with what we see in worms, that those segments without 
appendages or setze are the caudal ones. 
A prominent character of the higher worms is the annulations, or 
rings marking the body. In the Gephyrea, however, this feature is 
not so obvious as in the peduncle of Lingula, while in many of the 
lower worms, e. g., Chetognatha, Nematoidea, Acanthocephala, 
there are no segments, and in the Rotifera the segmentation is 
external. Therefore the absence of this character in the Brachio- 
poda is unimportant. | 
The presence of more than one segment in the Brachiopoda is 
possibly marked in Rhynchonella, where two pair of segmental 
organs, or oviducts, occur. In Lingula, also, a deep constriction 
occurs just back of the posterior occlusor muscles, a membraneous 
partition at this point tends to separate the perivisceral cavity, and 
the stomach has a corresponding ridge upon its walls. All these fea- 
tures certainly suggest segmentation. The arrangement of the 
muscles in Lingula into distinct sets, first the anterior occlusors, 
then the posterior occlusors, next the external, central and posterior 
adjustors, and finally the divaricator muscles, suggests segmentation 
of the body, as seen in the Arthropods. This feature is less marked 
in Discina, though still apparent, and with their external peduncular 
muscles one might, with propriety, theoretically form a number of 
rings. 
The dorsal and ventral symmetry is a distinctive character in worms. 
This symmetry is often so complete as to render the determination of 
above and below a 
Fig. 7. matter of great dif- 
ficulty, and, as in 
Sternaspis, a source 
of confusion. (See 
transverse section of 
Annelid, Figure 1.) 
The same feature 
is likewise charac- 
teristic of many 
Transverse section of Lingula. 
6. bands suspending intestine in perivisceral cavity. 7 = 
t. intestine. s. segmental organ. o. ovaries. J. Pe Brachiopoda d Leg 
er. g. gills. se, se. sete. ticularly with Lin- 
gula, where these 
regions externally are almost precisely alike, and where single valves 
of Lingula are found fossil, or their impressions are seen upon the 
