This section is from the book "General Outline Of The Organization Of The Animal Kingdom, And Manual Of Comparative Anatomy", by Thomas Rymer Jones. Also available from Amazon: A General Outline of the Animal Kingdom and Manual of Comparative Anatomy.
(1094). The muscular system of this animal is far more perfect in its arrangement than in the preceding classes, and the delicate fasciculi which move the rudimentary limbs are visible through the transparent integument (fig. 219.) In the abdomen, the muscles form longitudinal and transverse bands that intersect each other at right angles (fig. 221, d) - an arrangement not very different from what we shall soon meet with in the rotiferous animalcules.
(1095). The nervous system appears to consist prnicipally of two long filaments (fig. 221, c) that run beneath the alimentary canal: but it is extremely probable that these communicate with some minute ganglia in the neighbourhood of the head; at least, the perfect structure of the oral apparatus and the development of the limbs would seem to indicate such a type of structure.
(1096). The generative organs in the female Achiheres consist of two parts - the ovaria, wherein the eggs are formed, contained in the abdominal cavity (fig. 219, d d) - and of two external appendages, or egg-sacs (fig. 219, ff), which are attached to the posterior extremity of the body, for the purpose of containing the eggs until their complete development is accomplished: this arrangement we have already had an opportunity of examining in the Entomostracous Crustaceans.
Fig. 221. Viscera of Achiheres Percarum: a, alimentary canal; b, anal orifice; c, nervous filaments?; d, muscular bands; e, unimpregnated, and f, impregnated ovary; g g, external openings of the ovaria.
(1097). The internal ovaria (fig. 221, f), when distended with ova, occupy a great part of the cavity of the abdomen, and present a racemose appearance; but when empty, as represented upon the opposite side of the same figure (e), each is found to be a simple blind canal with sacculated walls, opening externally by an orifice (g g) through which the ova are expelled into the egg-sacs, where their development is completed.
(1098). It would seem that, even when the eggs are hatched, the excluded young are far from having attained their perfect or adult form, but undergo at least two preparatory changes or metamorphoses, during which they become possessed of external organs so totally different from those they were furnished with on leaving the egg, that it would be difficult to imagine them to be merely different states of existence through which the same animal passes.
(1099). On first quitting the egg, the young Achtheres is, in fact, by no means adapted to the parasitical life to which it is subsequently destined - possessing no organs of prehension like those of the adult, but merely two pairs of swimming-feet, each armed with a brush of minute hairs, and calculated to propel it through the water. Before, however, the first change is effected, another set of feet may be perceived through the transparent external covering, encased, as it were, in the first; when these are completely formed, the original skin falls off, displaying, in addition to the two new pairs of swimming-feet, three pairs adapted to prehension; and it is only when the second set of feet is thrown off in a similar manner that the animal assumes its perfect or mature form.
(1100). In Lamproglena pulchella we have a still more decided exemplification of the Crustacean type of structure, and the rudimentary feet, arranged in symmetrical pairs, are as numerous as the segments of the body. The limbs, however, are as yet only adapted to secure a firm hold upon the structures whereunto this parasite attaches itself, namely the gills of the Chub (Cyprinus Jeses), in which situation it is most usually found. The two anterior pairs (fig. 222, b, c) are far more largely developed than those which are placed upon the posterior parts of the animal, and are apparently strengthened by a cruciform cartilaginous framework, seen through the transparent integument. The first pair of these holding-feet consist of two robust and powerful hooks, terminated by simple horny points; whilst the second, which are likewise unciform, terminate in trifid prongs, and are evidently equally adapted to prehension. The four pairs of members that succeed to these are mere rudiments, and can be of little service as organs of attachment; but, to make up for their imperfection, we find at the posterior extremity of the body, between the orifices of the ovaria (g), a pair of cartilaginous suckers, well calculated to fix this part of the animal.
(1101). The muscular system is readily seen through the transparent skin: four longitudinal bands are visible (d), running from one end to the other; and, besides these, broad transverse fasciculi are discernible in the fifth and sixth segments of the body. From the nature of the feet, however, and general structure of the creature, we must imagine the existence of muscles provided for the movements of each articulated member, although, from their extreme minuteness, they escape detection.
(1102). The opening of the mouth is placed in the centre of the space bounded by the four anterior prehensile hooks; and the alimentary canal is a simple tube passing straight through the body to the tail, where the anal orifice is distinguishable. The walls of the intestine have a reticulated appearance, being covered with a kind of glandular network, that probably constitutes a biliary apparatus.
(1103). In a creature thus highly organized we may well expect to find senses of proportionate perfection; and in Lamjoroglena their existence is no longer doubtful. The eyes are distinctly apparent, of a reddish colour; but, as yet, as in the lowest Crustaceans, united into one mass. The antennae likewise, which may be regarded as special instruments of touch, are well developed, and, both in number and position, resemble those that characterize the Crustacean orders, to which we are thus conducted by almost imperceptible gradations.