256 



INVERTEBUATE MORPHOLOGY. 



the area enclosed by the lophophore. The nervous system 

 is exceedingly simple, consisting of a single ganglionic mass 

 (Figs. 114 and 115, ce) lying between the mouth and anus, 

 nerves ramifying from it to the various parts of the body. 

 The only sense-organs that have been detected are situated 

 upon the free portions of the body, more especially on the 

 lophophoral tentacles (t), and are represented by scattered 

 ectodermal cells each of which bears a strong cilium and is 

 in connection with a nerve-fibre ; they have been assigned a 

 tactile function, though it seems probable that they react to 

 stimuli of various kinds and have a much more generalized 

 function. 



The arrangement of the excretory and reproductive organs 

 varies considerably in different forms and may be more con- 

 veniently described in connection with the various orders. 



1. Order Endoprocta. 



This order contains but a small number of forms, which, 

 with one exception, Urnatella, are marine in habitat. They 

 all possess the power of reproducing 

 by budding, colonies being thus formed, 

 as in Pedicellina, Ascopodaria, and other 

 genera with the exception of Loxosoma, 

 in which the buds separate completely 

 from the parent at a relatively early 

 stage of their development. Each in- 

 dividual (Fig. 114) is a cup-shaped 

 structure, prolonged posteriorly into 

 a stalk {st) and upon the rim of the 

 cup, which represents the lophophoral 

 fold, or slightly below it on the inner 

 surface, the tentacles {t) are arranged 

 in a circle surrounding a depression, 

 the vestibule, into which open both 

 the mouth and the anus, the situation 

 of the latter opening within the circle 

 of tentacles having suggested the name 

 given to the order. The tentacles can 

 manner, so as to lie completely 



Fig. 114. — Sinolb Indi- 

 vidual OF Pedicellina 

 (after Nitsche). 

 ce = ganglion. 

 I = so-called liver. 

 « = stomach. 

 si — stalk. 

 t = tentacles. 



be coiled in a oircinate 



