186 



NA TUEAL HIS TOR Y. 



MACROBIOTUS HUFELANDI. 



ovate body, with faint indications of four segments, and upon each side four short conical limbs 



the hindmost of which occupy the posterior extremity. The mouth is suctorial, and consists of 

 a fleshy tube containing a pair of styliform organs, which can be protruded 

 and retracted by the action of muscles ; and the legs are terminated by threw 

 or four claws. No organs of circulation or respiration are recognisable in. 

 them. 



They have another peculiarity distinguishing them from all the other 

 Arachnida, namely, that they are absolutely hermaphrodite ; the single ovary 

 containing its eggs being always visible in the hinder part of the body, and 

 at the posterior end of it are placed the male organs, both sets opening 

 into a dilatation of the intestinal canal. In the course of the latter we see 

 towards the head a strongly muscular pharynx, followed by a veiy large 

 intestinal sac nearly filling the body, and surrounded by many small dilata- 

 tions, giving it a clustered appearance. The walls of this part are glandular, 

 and no doubt perform the functions of a liver ; and in addition to these there 

 are two large salivary glands which discharge their secretion into the mouth. 

 Curiously enough, the nervous system acquires a considerable development, 

 having fcmr large ventral ganglia with double commissures. On the sides of 

 the head there are a pair of eye-points. 



The systematic position of these curious little creatures was long a matter 

 of dispute, although, so long since as 1785, the Danish naturalist, O. F. 

 Miiller, recognised their affinity to the Mites, and described a species under 

 the name of Acarus iirsellus. They live sometimes in water, but more 



frequently in moss in damp places, and some of them are found 



especially in a rather curious locality, namely, the gutters of the 



roofs of houses. Like the Rotatorial animalcules which also occur 



in such places, the Tardigrada have the power of resisting desiccation. 



They may be found apparently quite dry among the sandy dust of 



a gutter, and will revive at once on being duly moistened. Their 



eggs, as may be seen from the figure, are of large comparative size 



and few in number, and they are generally deposited simultaneously 



with a change of skin of the parent animal, so that the cast skin serves 



as a protection to the young animals in hatching. The young resemble 



their parents, but are only about one-third the size. The known 



species are not very numerous. That figured is found in moss, and 



measures about one thirty-sixth of an inch in length. 



ORDER V. LINGUATULINA. 



If the Demodex folliculorum, which we have referred to the 

 Acaridse, be worm-like in its appearance, the same may be said with 

 still more force of the creatures belonging to the present order, which 

 indeed for a long time were always classed among the Entozoa. The 

 knowledge of their development, however, showed that they too were 

 most nearly related to the Arachnida, and of late years they have 

 taken their place among the aberrant forms of that class. 



In the mature state, the Linguatulina are vermiform creatures, 

 with a distinctly-ringed, and usually flattened, body, having at the 

 anterior end a mouth furnished with a horny ring, and on each side of 

 this two horny hooks, which can be protruded from small apertures. 

 Their form and the presence of these hooks led to the creatures being 

 regarded as allied to the Tape Worms. The male is usually much 

 smaller and shorter than the female. The intestine passes straight from the mouth to the other 

 end of the body, where the anal aperture is situated. Of the central nervous system, the principal 



PENTASTOMA T.KXIOIDES. 





