REPORT ON CORALS — HYDROCORALLIN^E. 27 



of other Hyclroids. They are figured by Professor Agassiz 1 as occurring in Millepora 

 aleiconiis. They are spheroidal in form, with transparent wall, and contents 

 composed of irregular granules, which are of a bright gamboge-yellow colour. It is 

 these cells which give the bright yellow tinge to the tips of . the living coral. The cell- 

 contents in these cells are frequently to be seen divided into two, each half having its 

 own nucleus, or sometimes more rarely into four (PI. XIV. fig. 9, b, c). The more 

 superficial part of the vascular network of the ccenosarc is in most places almost crammed 

 full of these pigmented cells, and they are abundantly present also within the somatic 

 cavities of the zooids. They become less abundant towards the deeper parts of the 

 living layer, and in certain of the deepest ramifications of the network are entirely 

 absent, their place being taken by transparent globules. In some parts of the hydro- 

 phyton large quantities of the pigmented cells are met with which arc coloured 

 dark brown instead of yellow. These belong probably to the older parts of the coral, 

 which have in the living condition a brown appearance, it being only the growing tips 

 which are bright yellow. Such, however, was not ascertained to be the case. 



At the under surface of the living layer of the hydrophyton the ccenosarcal network 

 has in connection with it, or is prolonged into, a network of extremely transparent thin- 

 walled vessels, many of which terminate in blind extremities, as shown in Plate XIV. 

 fig. 8, B. These vessels are distended with small exceedingly transparent and highly 

 refractile globules, without any admixture of pigmented cells. These transparent 

 globules are found scattered amongst the pigmented cells throughout the vessels of the 

 ccenosarc, but occur in masses only as above described. No clue to the function of these 

 transparent globules, nor explanation of their being thus agglomerated in the deeper 

 parts of the living layer, was obtained ; the masses of them probably point to a fatty 

 degeneration of the effete deep regions of the network of the ccenosarc. 



Nematocysts. — The nematocysts are of two kinds. They are shown, carefully drawn 

 to measurement, in Plate XIII. figs. 1 and 2. One kind is that which appears to be 

 confined to Hydrozoa, and not to occur at all in Anthozoa, viz., that in which a bladder- 

 like enlargement of the thread occurs at that part of it which is immediately next the 

 mouth of the cell, the bladder being armed near its summit by three spines set in one 

 whorl. The three spines in this form of nematocyst in Millepora are remarkably long, 

 and directed at right angles to the axis of the thread, instead of recurved, as usual. 

 These nematocyst vary very much in size. The one figured is one of the largest 

 observed, being of about two-thirds of the length of the ovoid nematocysts. The larger 

 examples of these three-spined nematocysts are of comparatively rare occurrence, only 

 a few being present in some of the tentacles, and being more commonly present in the 

 tentacles of the gastrozooids. The smaller nematocysts of this form have not more 

 than l-6th of the length of the larger ones. They form the bulk of the spheroidal 



1 Loc. cit., plate xv. fig. 5. 



