Chap. IV. 



TUBULARIA COUTHOUYI. 



267 



As regards the details of the anatomy of this hydroid, what has been said of 

 Parypha crocea (p. 250) might be repeated here, with a few modifications, which 

 we will now point out. The proboscidal tentacles, not less than fifty, in the 

 oldest hydroids, do not all take part in the formation of the converging ridges 

 which run to the mouth, but only those of the uppermost series, while the bases 

 of the others are merged into the proboscis lower down. The ridges which are 

 formed by their decurrent bases project to a quarter or less distance down 

 the proboscis, according to the size of the tentacles from which they originate 

 {Fig. 4, a). 



Below the terminal globose expansion of the stem, the interior wall has a very 

 remarkable structure, which has no parallel in any other of the Hydroids. Upon 

 making a careful transverse section with a very sharp scalpel, we were surprised 

 to find that at least two thirds of the stem within the boundary of the outer 

 Avail is filled by a solid central mass, composed entirely of large polygonal cells 

 (PI. XXIIP. Fig. 8, y*). At the periphery of this mass, there are several longitudinal 

 channels (/ j^), disposed at pretty regular intervals, and varying in number, according 

 to the age of the hydroid, from fourteen downwards. One of these channels {j^) 

 is always much larger than the others, and is equal to one fourth the diameter 

 of the whole cellular mass {d g*), while the smaller ones (/) have one half this 

 diameter. The larger channel is the only one present during the earliest period 

 of growth of the young hydroid, and at that time constitutes the broad chymif- 

 erous cavity of the stem. Unlike the smaller channels, it extends for the whole 

 length of the stem, in unbroken continuity, and has, in its course, no connection 

 whatsoever with them ; whereas the smaller channels fork, from time to time, as 

 they pass upward, thus increasing in number according to the age and length of 

 the stem. All these channels may be seen with the naked eye (PI. XXIV. Fig. 1); 

 but with a low magnifying power the difference between the larger channel 

 [Fig. 1", «') and the smaller ones (a) becomes very apparent.^ The large channel 

 varies from cylindrical to broadly ovate, and in the latter case the broader diameter 

 trends toward the axis of the stem. The smaller channels (PI. XXIIP. Fig. 8, j) 

 are broader, in a direction trending toward the axis of the stem, than they are 



' We find the large, and the small channels 

 also, in a very closely related species, the Tubtilaria 

 indivisa of Europe, sent to us by Sars from the 

 coast of Norway ; and if the observations of Dr. 

 T. S. Wright, which are published in the Edin- 

 burgh New Philosophical Journal for January, 1858, 

 p. 113, PI. III. Figs. 2 and 3, were made upon 

 this same species, then his discovery, although very 



interesting, was only a partial one. It hardly seems 

 possible that he could have noticed the channels, 

 from the outside of the stem, without seeing also 

 the single large one, which is very conspicuous, 

 and thus have been led to inquire into the cause 

 of this difference by a more careful section than 

 the crushing blades of a pair of scissors, however 

 sharp, would afford. 



