parasitic within recent Madreporaria. 245 



Y. The Parasitic Canals near the eccterior and their Methods of entry : 

 jReproductive Elements. 



The finer canals and those of all diameters except the very smallest may- 

 be occasionally traced to the outside of the hard coral-structure, so that 

 the method of entry of the parasite can be determined. This is greatly 

 assisted by decalcifying, after noting the character of the vegetation, which 

 is inseparable, except by tearing, from the wall of the specimen. 



Methods of entry. — 1. Earely a long typical canal may be seen opening 

 out through the coral-wall without any increase of caHbre. 



2. Dark globular or short cylindrical-shaped cavities exist in the very 

 outside of the theca, and usually in such positions where the external 

 ornamentation or where the intercostal spaces admit of substances resting 

 readily. The cavities are large, and vary from to y-oVu i^*^^ 

 meter ; their contents give a dark and opaque appearance to them, and 

 they give off many very fine short canals, canals of larger calibre which 

 pass more or less inwards, and the common long ramifying and non- 

 inosculating canals, there being one or many of these (Plate 5. figs. 1-7 

 & 10). 



3. Long, straight, and also curved canals of large calibre, to Yrhu 

 inch, usually constricted here and there, and in some instances having 

 hemispherical projections. They sometimes pass far inwards (Plate 5. 

 fig. 8), and then their contents are usually not so crowded as to prevent 

 light being transmitted ; and, indeed, in one specimen long portions of the 

 canal were deficient in granular, and were filled with homogeneous and 

 clear cytioplasm. Sometimes the wide canal ends in a cul-de-sac; but in 

 most instances smaller canals pass off irregularly from it, and even some 

 of the minutest. 



4. Irregular excavations occur on the surface of the coral of no great 

 depth, into which shallow cup-shaped depressions enter ; and these are 

 either with sharp edges and give entry to a typical tube or to many fine 

 and short tubes in addition (fig. 10). 



There is in a specimen of Flahellum laciniatum a tunnel reaching in- 

 wards from one of these irregular excavations which has three more or 

 less globular enlargements on it, the last being continuous Avith a very 

 short prolongation of the tube. 



5. Great numbers of very branching canals form a close network and 

 extend into the coral-structure, usually from the top of a costal or septal 

 ornament, in BalanopJiylUa verrucaria for instance. These glomeruli arise 

 from a depression in the outside of the coral, or from a decided large 

 penetration, and it appears as if a mass of oospores had collected therein 

 and germinated (Plate 5. fig. 1). 



Transverse sections, of necessity, cut through these masses of branching 

 and anastomosing tubes at different angles ; and it is possible, therefore, 

 by comparing numbers from the same coral to estimate the length of a 

 mass and to recognize the typical canals which eventually arise from it. 



