With the cysts of Cysticercus pisiformis, s. C. Taeniae serratae.
In the upper part of this preparation is suspended a portion of the great omentum of a Rabbit (Lepus cuniculus). Seven pyriform sacs may be observed attached to it, a group of three on the left-hand side and a fourth at the right-hand corner being especially conspicuous. These sacs are connective tissue cysts which lodge each a single individual and rarely more of the cystic stage (Cysticercus pisiformis) of T. serrata. See next preparation. The presence of the parasite, like the presence of any other foreign body, has had an irritating effect on the tissues of the omentum, and the consequence is the formation of a protective capsule. The brain and the eye are the only two parts of the body in which this capsule is never formed.
In the lower part of the preparation is suspended a Tapeworm, Tcenia serrata, which inhabits the intestines of the dog. When a dog devours a rabbit, and swallows an encapsuled Cysticercus pisiformis, the head and neck of the latter develop into the Tapeworm, as it is seen here. The head and neck are displayed in the middle line, bent forwards and downwards. With the aid of a simple lens the head may be seen to possess a slight median projection, the rostellum, at the base of which is a circlet of chitinous hooks. The possession of these hooks constitutes the difference between an 'armed' and an 'unarmed' Tapeworm. 'Unarmed' Tapeworms are not found in the Carnivora. The head expands below the hooks, and bears four rounded pit-like suckers, one of which is turned towards the observer. It then contracts into a short unjointed neck. The neck begins to broaden out into the body of the worm, and it is at the same time divided by transverse lines into a series of joints. The first joints are almost linear: they then become broader and deeper, and finally their depth becomes greater than their breadth. Their posterior margin becomes at the same time remarkably prominent. The two last joints are of considerable length and comparative narrowness.
They are ripe and ready to be detached.
If the lateral margins of the joints are attentively examined, one or other is seen to present near its centre a prominent papilla. This papilla is the projecting edge of the porus genitalis. It alternates generally, but not invariably, in succeeding joints from the right to the left side.
The head and neck are often termed 'scolex,' the joints, 'proglottides,' and the whole Tapeworm, 'strobila.'
There are five Tapeworms ordinarily found in the intestines of the dog. Of these, Taenia Echinococcus, derived from the cystic form Echinococcus veterinorum, which occurs in a variety of Mammals, consists as a rule only of a head and neck with three or, at the utmost, four joints. It is not much longer than an intestinal villus. Taenia elliptica, derived from the Cysticercus T. ellipticae, which inhabits the dog-louse (Trichodectes Cam's), is recognisable at once by the elliptic shape of its ripe joints and the two pori genitales, one right and the other left. It also possesses a peculiar round rostellum beset with four irregular rows of sixty small hooks. The other three Tapeworms are not so easy to distinguish. They are T. serrata, derived from the C. pisiformis of the Rabbit; T. marginata, from the C. tenuicollis of the Sheep, etc.; and T. coenurus, from Coenurus cerebralis of the Sheep, and perhaps of the Rabbit.
T. serrata has the largest head (1.3 mm.), and a circle of 38-48 hooks, alternately large and small, the large hooks being 25 mm. long, and the length of the anterior branch of their forked roots very great; the proglottis, when ripe, is 8 mm. long and 3 mm. broad; the uterus, when full of ova, has 8-10 main lateral branches beset with numerous short ampullae. There are about 325 joints between the neck and the first ripe joint.
T. marginata has scarcely any constriction behind the head: the number of hooks is 22-42, the hooks being smaller than those of T. serrata: the proglottis is larger and longer; the uterus has about eight side branches which are much branched laterally. There are about 510 joints in front of the first ripe joint.
T. coenurus has a pyriform head; 24-32 hooks, which are small; the proglottis is smaller than that of T. serrata; the uterus has 20-25 simple branches. There are about 200 joints before the first ripe joint.
The egg-shell of all three is about .027 mm. in diameter, but in T. serrata it rarely bears processes as it does in T. marginata.
The rostellum of Taeniae often attains a greater size than it does in T. serrata. It has a special system of muscles. The same is true of the suckers which are composed of radial and equatorial fibres almost exclusively. The former deepen the cup, the latter contract its margin.
The surface of a Tapeworm is bounded by a vertically striated cuticula which, according to Griesbach, is a product of the gelatinous connective tissue of the body. The striae are due to poresl. Beneath the cuticle is a system of transverse or circular fibres which Leuckart considers to be muscular; Griesbach as elastic. The substance of the body in Solenophorus consists of a gelatinous matrix which forms a system of trabeculae with lacunar spaces representing the coelome. The matrix contains elastic fibres and nuclei, small rounded, as well as stellate cells, and therefore closely resembles the connective tissue of Mollusca (Griesbach). A fine granular protoplasm with nuclei (? cellular: see infra under T. lineata) covers the trabecula immediately below the cuticula, but does not appear to extend continuously into deeper strata. There is a thin superficial layer of longitudinal muscles and two deeper layers, an outer of longitudinal and an inner of circular fibres, as well as a system of dorso-ventral fibres.
The deep longitudinal and circular layers surround a nucleus or core of connective tissue which lodges the generative organs, the longitudinal excretory canals, and longitudinal nerves.
1 It has been said that protoplasmic processes extend into these pores from the granular protoplasm covering the subjacent connective tissue trabeculae.