IIG A. OKA. 



part. ITow the nerve fibres, if there he any, pass ont from the latter 

 into the nerve-trunhs, I have 1)een unal)le to ehicidate. 



Tlic cross-section of the lophoplioral nerve trunk is kidney- 

 sh;ip('(h with the concavity tnrned above (fig. 31, PI. XIX. nrrr('). 

 In it tlie nuclei of nerve-cells are seen mnch crowded. Longitudinnl 

 sections show that the nerve-cells in cpiestion are spindle-shajx^i 

 (bipolar) with the nucleus at the middle, and closely packed tog-ether. 

 A few fil)rcs run amongst them ; these are probably to be regarded as 

 nerve-fibres. The trunks themselves are very thick and large 

 in companson wifh the mass of the central ganglion, and their 

 structnre gives the impression of an elongated ganglionic mass rather 

 than of a nerve. The trunk gives off on each side a branch into each 

 tentacle. Such a branch is of fibrous appearance and could be 

 traced onlv for a very short distance after its de])arture fi-oui the 

 trunk. 



The presence of a circumcesophageal nervous commissure in 

 fresh-water Polyzoa is a matter of obscurit}^ having been accepted by 

 a few and denied by many. My observations on Pect, gdathinsa 

 convinced me of its absence. 



T'he colonial nervous system present in many marine Polyzoa, 

 wliich keeps the action of the members of a colony in har- 

 mony, seems to be altogether wanting in this species, as is probably 

 the case in all other fresh-water Polyzoa. Special attention to 

 tliis point showed no trace of nervous connections between the 

 polypides in ])reparations of sectioned colonies. The fvct agrees with 

 the behavior of the p(^lypides in a living colony, in which only 

 directly disturbed polypides retract, while all the rest remain pro- 

 truded as if nothing had liappened. 



