Prosoma

“ This marginal rim is composed of a single row of flat, oblong, elevated structures (see fig. 44, a) ; it is narrow at the genal angles and is not developed on the posterior edge. Apart from this ornamented rim, the prosoma is smooth.
The compound eyes are not preserved except for the barely perceptible anterior margin of the left eye and a slight elevation that
may represent the eye node. The node is probably arcuate, and the palpebral lobe covers most of the eye. The prosoma measures 69 mm. in length, 79 mm. in width behind the compound eyes, and 99 mm. ”

“ The prosoma is very wide, forming an almost perfect parabola, and is straight along the base. The lateral eyes are small and crescentic, and are covered by a conspicuous palpebral lobe; they are located slightly behind the center of the carapace and closer to each other than to the lateral margins (see figs. 48–50, 52) . ”

“ The thorax and prosoma are of the same shape as in I. Cumingii, and in the largest specimen, about one tenth of an inch square; the prosoma, as in that species, is hairy. In the Mouth, all the parts are closely similar to those of I. Cumingii, but one third larger; the crest of the labrum is a little roughened with minute points: the palpi are squarer and blunter at their extremities: the mandibles have their second and third teeth nearly equal in size to the first, and they do not appear pectinated: the maxillæ have their spinose edge very nearly straight: the outer maxillæ are pointed. ”

“ The three posterior pairs are remarkable from the pairs of main spines being placed so close one under the other, and in an oblique direction, that at first they appear to form a single crowded transverse row: the dorsal tufts are rather large.
Body.—The body is remarkable from its nearly vertical position, and from the much elongated pyramidal form of the prosoma, extending down nearly to the bottom of the sack. The membrane investing the prosoma, presents a few circular folds, falsely appearing like articulations. The œsophagus enters the stomach rather obliquely. ”

“ EU-ARACHNIDA.—These start from highly developed and specialized aquatic branchiferous forms, exhibiting a prosoma with six pediform pairs of appendages, an intermediate prae-genital somite, a mesosoma of six somites bearing lamelliform pairs of appendages, and a metasoma of six somites devoid of appendages, and the last provided with a post-anal spine. Median eyes are present, which are monomeniscous, with distinct retinal and corneagenous cell-layers, and placed centrally on the prosoma. ”

“ Following the prosoma is a region consisting of six segments (figs. 14 and 15) , each carrying a pair of plate-like appendages in both Limulus and Scorpio. This region is called the mesosoma. The tergites of this region and those of the following region, the metasoma, are fused to form a second or posterior carapace in Limulus, whilst remaining free in Scorpio. The first pair of foliaceous appendages in each animal is the genital operculum; beneath it are found the openings of the genital ducts. The second pair of mesosomatic appendages in Scorpio are known as the “pectens.” ”

“ An internal skeletal plate, the so-called “entosternite” of fibro-cartilaginous tissue, to which many muscles are attached, is placed between the nerve-cords and the alimentary tract in the prosoma of the larger forms (Limulus, Scorpio, Mygale) . In the same and other leading forms a pair of much-coiled glandular tubes, the coxal glands (coelomocoels in origin) , is found with a duct opening on the coxa of the fifth pair of appendages of the prosoma. The vascular system is highly developed (in the non-degenerate forms) ; large arterial branches closely accompany or envelop the chief nerves ”

“ The segmentation of the prosoma and the form of the appendages bear a homoplastic similarity to the head, pro-, meso-, and meta-thorax of a Hexapod with mandibles, maxillary palps and three pairs of walking legs; while the opisthosoma agrees in form and number of somites with the abdomen of a Hexapod, and the tracheal stigmata present certain agreements in the two cases. ”

“ Shape of Body, Sack, Colours, &c.—From the position of the orifice of the capitulum, the animal’s body is suspended to the scuta in a more transverse direction than is usual. The prosoma is well-developed, and is distinctly separated from the three posterior thoracic segments, [Pg 311] by a band of thin membrane. The tunic of the basal part of the sack, where it enters the peduncle in a blunt point, is thickened and covered with roughened rounded papillæ. The corium of the sack under the valves, is coloured (after spirits) so dark a brown as to be nearly black ”

“ Opisthosoma confluent throughout its breadth with the prosoma, with the dorsal plate of which its anterior tergal plates are more or less fused; at most ten opisthosomatic somites traceable; the generative aperture thrust far forwards between the basal segments of the 6th appendages. Prae-genital somite suppressed. Respiratory organs tracheal, opening by a pair of stigmata situated immediately behind the basal segments of the 6th pair of appendages on what is probably the sternum of the 2nd opisthosomatic somite and also in some cases upon the 5th segment of the legs. ”

“ Genus Parastylonurus, new genus
Diagnosis.—Stylonuridae of small to medium size; prosoma rounded-quadrate; wider than long, with lateral eyes, arcuate and located on anterior half of the carapace; metastoma very long, with deep triangular notch or deeply cordate and with base truncated; first three walking legs very short with single opposable spines on each joint; last two walking legs very long, reaching to the last tergite; podomere-count: ?–?–7?–8–9–9; ornamentation consists of scales; opisthosoma narrow, undifferentiated ”

“ Besides these muscles of attachment, the prosoma is furnished with several other muscles. There are superficial muscles running up towards the basal margin of the sides of the mouth; and other deeper muscles, to which, I presume, the movements of the mouth, as a whole, are due. The muscles moving the gnathites do not, as far as I could make out, extend beneath the basal edge of the mouth. ”

“ Urotricha.—Dorsal area of prosoma covered with a single shield (? two in Geralinura) , bearing median and lateral eyes. Post-anal sclerite modified as a long, many-jointed feeler. Appendages of 2nd pair folding in a horizontal plane, completely chelate, the claw immovably united to the sixth segment. Respiratory organs present in the form of pulmonary sacs. ”

“ Concentration of the organ-systems by fusion of neighbouring regions (prosoma, mesosoma, metasoma) , previously distinct, has frequently occurred, together with obliteration of the muscular and chitinous structures indicative of distinct somites. This concentration and obliteration of somites, often accompanied by dislocation of important segmental structures (such as appendages and nerve-ganglia) , may lead to highly developed specialization (individuation, H. Spencer) , as in the Araneae and Opiliones, and, on the other hand, may terminate in simplification and degeneration, as in the Acari. ”

“ In this prosomatic region, we find in Limulus the same tripartite division of the nerves as in the mesosomatic region, so that the nerves to each segment may be classed as (1) appendage-nerve; (2) sensory or dorsal somatic nerve, supplying the prosomatic carapace; (3) motor or ventral somatic nerve, supplying the muscles of the prosoma, and containing possibly some sensory fibres. ”

“ Ibla Cumingii, female, (magnified about five times) , with the right hand valves and right side of the peduncle removed. The Male (h) is seen attached in the sack. The peculiar form of the body, caused by the small development of the prosoma, by the distance of the first and second pairs of cirri, and by the distance of the mouth from the adductor muscle, (a dark dotted circle opposite i,) and lastly, the remarkable course of the œsophagus over the adductor muscle, together with the outline of the stomach, are here all exhibited. ”

“ Their movement in an upward or downward direction in Limulus and Mygale must exert a pumping action on the blood contained in the dorsal arteries and the ventral veins respectively. In Scorpio the completion of the horizontal plate by oblique naps, so as to form an actual diaphragm shutting off the cavity of the prosoma from the rest of the body, possibly gives to the organs contained in the anterior chamber a physiological advantage in respect of the supply of arterial blood and its separation from the venous blood of the mesosoma. ”

“ The following species are recognized for this genus:
Genus Strobilopterus Ruedemann, 1935
Diagnosis.—Dolichopteridae of medium size; test covered with pustules and semi-lunar scales; prosoma semiovate; compound eyes submarginal; ocelli unknown; ventral doublure unknown; sixth appendages with movable, supplementary flat lobes on distal joints, ultimate joint forming large, flat lobe; distal joints and lobes forming paddle with strongly serrate margin; metastoma very narrow, cordate at anterior end; base unknown; male median appendage very long, consisting of one undivided joint ”

“ This interpretation, however, of the “metasternites” of Limulus and Scorpio is opposed by the coexistence in Thelyphonus (figs. 55, 57 and 58) of a similar metasternite with a complete praegenital somite. H.J. Hansen (10) has recognized that the “praegenital somite” persists in a rudimentary condition, forming a “waist” to the series of somites in the Pedipalpi and Araneae. The present writer is of opinion that it will be found most convenient to treat this evanescent somite as something special, and not to attempt to reckon it to either the prosoma or the mesosoma. ”

“ Fig. 162.—Eurypterus fischeri, Eichw. Upper Silurian, Rootziküll, Oesel. Restoration of ventral surface; 1–6, appendages of prosoma; m, metastoma. Immediately posterior to the metastoma is the “median process” of the genital operculum. (After Holm.)
287The fifth appendage is longer than the fourth and is directed backwards; its second and third joints are short and ring-like; the others (fourth to eighth) are long and similar to one another, each being of uniform width throughout; the last joint is produced into a spine on each side, and between these two is the movable end-spine ”

“ Although the linear form and the elongation of the body are common to the stick-Insects and the Proscopides, yet this structure is due to the growth of different parts in the two families. In the Phasmidae the prothorax is small, the mesothorax elongate, while in the Proscopides the reverse is the case. The elongation of the head is very curious in these Insects; the mouth is not thus brought any nearer to the front, but is placed on the under side of the head, quite close to the thorax. ”

“ Owing to these peculiarities it was for long assumed that the species of Prosopis must be parasites. This is, however, known not to be the case so far as many of the species are concerned. They form cells lined with a silken membrane in the stems of brambles and other plants that are suitable, or in burrows in the earth, or in the mortar of walls; individuals of the same species varying much as to the nidus they select. The food they store in these cells is much more liquid than usual, and has been supposed to be entirely honey, since they have no apparatus for carrying pollen. ”

“ The middle region of the body bears notopodeal fasciæ of long, fine, simple, natatory setae in addition to the compound neuropodials. The appendage of the compound setae differs from that of californiensis in having the accessory tooth farther distad, well beyond the middle of the concave edge, whereas in the other species it is normally rather proximad of the middle. In the present species the prostomium is proportionately larger, less covered by the peristomial flap which does not extend over the base of the median tentacle. The palpi are not fused so far distad, being united only at base ”