Fig. 33.—Separate scolex, or echinococcus-head. Magnified 500 diameters. After Huxley.
In the completely developed state the echinococcus-heads exhibit somewhat variable characters as to size and form, the latter differences being, for the most part, dependent upon their degree of contraction and vitality. In the perfect condition they vary from the 1/60″ to the 1/100″ in diameter, being usually about the 1/80″. They are solid, and when stretched out exhibit an hour-glass-like constriction at the centre of the body, which divides the scolex into an anterior part supporting the rostellum and suckers, and a posterior part which has been compared to the caudal vesicle of ordinary Cysticerci. The rostellum supports a double crown of hooks, but the disparity of the two series is scarcely sufficiently marked to render their distinction obvious. The hooks of the smaller row vary in size from 1/1040″ to 1/830″ of an inch, whilst those of the larger series are from 1/830 to 1/555″. In all instances the root-processes are incompletely developed, and consequently vary in thickness. They are, as Leuckart also has stated, apt to exhibit abnormalities.
In regard to the development of the echinococcus-heads it further remains for me to observe that a distinct water-vascular system is recognisable in the scolices. By the intervention of the pedicle of the scolex this system is connected with the brood-capsule, and also with the vessels of the maternal endocyst. In the scolex there exists a circular channel immediately below the rostellum, and this ring, on either side, gives off two vessels which pass downwards in a tortuous manner, internally, until they arrive at the pedicle where they unite to form two channels, which latter are continued into the vascular system of the maternal endocyst. In the retracted condition their position, of course, becomes very much altered, and they form loops on either side of the central line which marks the space leading down to the inverted head. Neither Prof. Huxley nor myself have seen these vessels, which Leuckart observed in the scolex itself, but Huxley discerned some apparently loose cilia in the granular parenchyma of the body; their longitudinal measurement being about the 1/3500 of an inch.
Fig. 34.—An Echinococcus brood-capsule (flattened by pressure). Magnified about 120 diameters. From a drawing by Professor Busk.
As regards the production of “nurses” by the phenomenon of proliferation, I can only remark that the endocyst is primarily concerned. The secondary and tertiary vesicles must be regarded as so many special bud-developments which, instead of becoming brood-capsules, become daughter-vesicles and grand-daughter vesicles, constantly developing in their interior secondary and tertiary brood-capsules and scolices, but sometimes, it would appear, developing neither the one nor the other. This is the view of Naunyn, which is somewhat opposed by Leuckart, who holds that the vesicles ordinarily arise from within the layers of the ectocyst. Speaking of these daughter-hydatids Leuckart remarks that “Naunyn denies that they take their origin between the lamellæ of the mother bladder—a fact, however, which, in agreement with Kuhl and Davaine, I have seen more than once and have followed out step by step.” For my own part I incline to the belief that the process as observed by Leuckart is exceptional, and that under ordinary circumstances it occurs as Naunyn has described it. Thus the long and short of the whole matter appears to be that the endocyst is capable of forming solitary scolices. Some of the scolices become differentiated to form brood-capsules, a portion of whose individual echinococcus-heads may, in their turn, become secondary brood-capsules, whilst others fail to become either scolices or brood-capsules. It accords with our knowledge of the general plan of development to believe that the daughter and grand-daughter hydatids are likewise peculiarly modified scolices. They are, in short, buds of the endocyst.
The distribution of hydatids throughout the organs of the bearer, and their prevalence in particular countries, has especially engaged my attention. I have personally examined upwards of a thousand preparations of entozoa in our public collections; and of these, 788 are preserved in the anatomical and pathological museums of the metropolis. By this inspection I have obtained a tolerably accurate knowledge of the pathology, localisation and effects produced by the presence of bladder-worms in at least 200 unpublished cases of hydatid disease. Most of our museums exhibit one or more specimens that are unique. After making certain necessary deductions, I find that I have 192 new cases to add to the 135 cases of hydatid disease that I had previously recorded, affording a total of 327 cases available for statistical purposes. If an analysis of these cases be made and compared with the statistics furnished by Davaine, and if the whole be reduced to the lowest number of practically available terms, we at length obtain a result which, although it may be only approximatively correct, is nevertheless of much practical value and significance. The statistics in question stand as follows:
| Organs affected. | Davaine. | Cobbold. | Total. |
|---|---|---|---|
| Liver | 165 | 161 | 326 |
| Abdomen, including spleen | 26 | 45 | 71 |
| Lungs | 40 | 22 | 62 |
| Kidney and bladder | 30 | 23 | 53 |
| Brain | 20 | 22 | 42 |
| Bones | 17 | 16 | 33 |
| Heart and pulmonary vessels | 12 | 13 | 25 |
| Miscellaneous | 63 | 25 | 88 |
| Total | 373 | 327 | 700 |