MR. H. N. MOSELEY ON THE STRUCTURE OF THE STYLASTERIDH3. 
469 
G. 0 . Sars, who is the only naturalist who has observed a Stylasterid alive, never 
saw the zooids raise themselves above the levels of the mouths of their cyclo-systems. 
In the building up of the corallum, which must be deposited, as in Millepora, by 
the ectodermal covering of the coenosarcal canals, absorption of already formed hard 
structures must take place during the gradual increase in size of the ampullae and the 
widening of canals, which, as shown in the figures, are larger in bore in the deeper 
than in the younger superficial regions of the corallum. A re-deposit must also take 
place constantly, for old ampullae, in the deeper parts of the coralla, are to be found in 
all stages of obliteration. Sometimes in some genera a rejuvenescence of parts of the 
corallum takes place ; a previously dead area becoming overgrown from its margins by 
a living lamina, which spreads over and covers it. 
Parasites. 
The coralla of nearly all Stylasteridae are liable to become much distorted in growth 
by the presence upon them of parasites of various kinds, each of which appears by the 
special kind of irritation which it offers to produce a particular form of abnormal 
growth in the part of the corallum it infests, producing thus, as it were, an animal 
gall. The commonest distortion is the reduction of the stem of a coral or branch, or 
of one side of these, into a hollow canal or deep furrow, more or less roofed over by a 
thin wall. This condition is produced by the adherence to the growing stem of an 
Aphroditacean Annelid. It has been noticed and described by Count de Pourtales 
and Verrill, in St plaster erubecsens and Allopora Californica. I have seen it in 
Cryptohelia, St plaster, Allopora, and Errina. On Errina labiata , a parasitic filiform 
Nemertean also occurs which twines itself round the tips of the branches in many 
coils. The branches thus irritated grow out into a burr-like mass of projecting points 
which are evidently hypertrophied clactylopore prominences, and sometimes assume 
almost the appearance of the normal spines of Spinipora. 
The most interesting parasite observed was a form found in the gastric cavities 
of the gastrozooids of PliobotJvrus symmetricus contained in small capsules. These 
were badly preserved, but there seemed little doubt that they contained the remains 
of larvae of a Pycnogonid, so that the deep-sea Pycnogonids, which are so abundant, 
very possibly pass their early stages in deep-sea Stylasteridae. The formation of a 
calcareous corallum has not vitiated the capabilities of the Stylasterid Hy droids as 
hosts for Pycnogonid larvae. The gastrozooids containing the larvae were partly 
aborted. 
Classification. 
I place the Stylasteridae with the Milleporidae in a separate sub-order of the 
Hydroids, which I term Hydrocorallinae, in accordance with a suggestion which I 
* Bull. Mus. Comp. Zool., Harvard, VI., p. 136. 
