CLADOCARPUS DOLICHOTHECA. 51 
marked character. The parts of the rachis to which the backs of the hydro- 
thece are applied are divided, by imperfect septa (septal ridges), into 
numerous very distinct chambers, while a few similar ridges also project 
into the cavity of the intervening portion. 
Where the stem ceases to give off pinne, it becomes divided into three 
or four internodes by very oblique joints, so as to assume, for some way 
down, the appearance of being twisted, and then continues towards the 
hydrorhiza as a simple continuous tube (Fig. 5). Along nearly the whole of 
its course from the termination of the pinnate portion to the base, the stem 
carries a longitudinal series of tubular nematophores, which are situated 
at short and equal intervals from one another, and give to this part of the 
hydrosoma a close resemblance to certain forms of graptolites.* 
The phylactogonia, or protective appendages of the reproductive cap- 
sules, resemble in form the antlers of a stag. Their branches are set with 
large tubular nematophores. They arch over the front of the stem, their 
branches crossing one another from opposite sides, and forming a cage-like 
roof over the gonangia. They occur only on some of the pinne, which are 
situated close to the distal end of the stem, one springing from each pinna 
close to its origin. Though the pinne which carry them retain their normal 
form, they are all more or less shortened, most of them supporting only 
a single hydrotheca. 
It is difficult to form any well-founded opinion as to the exact homology 
of these appendages. The nature of the changes which have resulted in the 
formation of a corbula in certain species of Aglaophenia might lead us to 
suspect that in Cladocarpus dolichotheca the phylactogonium represents the 
mesial nematophore of the proximal hydrotheca of its supporting pinna. 
The fact, however, that this nematophore is at the same time present in its 
normal state renders such an explanation untenable. The phylactogonium 
probably represents, in a greatly modified condition, the mesial nematophore 
of a hydrotheca, which had itself been totally suppressed. 
The sex of the gonophores could not be determined in the specimen. 
* T have elsewhere (Gymnoblastic Hydroids, p. 176) endeavored to show the probability that the den- 
ticles of graptolites represent the nematophores of the Plumularide, the hydrothecze being entirely sup- 
pressed; and I have attempted to support this view on both anatomical and embryological grounds. As 
the nematophores of the Plumularide are filled with sarcode capable of a rich development of pseudopodia, 
the graptolites would by this comparison be brought into close relation with the Rhizopoda. They would 
thus represent an ancestral form in which the affinities looked on one side to the Hydroida, and on the 
other to the Rhizopoda. No hydranths were developed in them, for the hydroid characters had not yet 
gained that ascendency over the rhizopodal which we see in the existing Plumularid, which, according to 
this hypothesis, have inherited their nematophores from the extinct graptolites. 
