. The Cambridge natural history. Zoology. DEVELOPMENT AFFINITIES 483. The segmentation of the egg in M. macronyx is total and equal, according to the observations of von Erlanger.' A blastvila, foUovs^ed by a gastrula, is formed. The blastopore closes, but later the anus appears at the same spot. There are four pairs of mesodermic diverticula which give rise to the coelom and the chief muscles. The reproductive organs arise as an unpaired diverticulum of the aKmentary canal, vchich also gives origin to the Malpighian tubules. The development is thus very primi- tive and simple, and affords no
. The Cambridge natural history. Zoology. DEVELOPMENT AFFINITIES 483. The segmentation of the egg in M. macronyx is total and equal, according to the observations of von Erlanger.' A blastvila, foUovs^ed by a gastrula, is formed. The blastopore closes, but later the anus appears at the same spot. There are four pairs of mesodermic diverticula which give rise to the coelom and the chief muscles. The reproductive organs arise as an unpaired diverticulum of the aKmentary canal, vchich also gives origin to the Malpighian tubules. The development is thus very primi- tive and simple, and affords no evidence of degeneration. "With regard to their position in the animal kingdom, M^riters on the Tardigrada are by no meanq ao-repd O V Miillpr ^"'- 254.—Male reproductive organs of means agreea. u. £. muiier MacmUotus hvfdancu, c. Scii., x placed them with the Mites; about 350. (From Plate.) ^, Epi- ci 1 -,. T -ni 1 .1 dermal thickening round anns; cL bchultze and Ehrenberg near the cloaca; , accessory gland; , Crustacea : Duiardin and Doyere Malpighian gland; st, stomach ; te, . testis; x, mother-cells of spermatozoa. With the Kotiiers near the Annelids; and von Graff with the Myzostomidae and the Pentastomida. Plate regards them as the lowest of all air- breathing Arthropods, but he carefully guards himself against the view that they retain the structure of the original Tracheates from which later forms have been derived. He looks upon Tardigrades as a side twig of the great Tracheate branch, but a twig which arises nearer the base of the branch than any other existing forms. These animals seem certainly to belong to the Arthropod phylum, inasmuch as they are segmented, have feet ending in claws, Malpighian tubules, and an entire absence of cilia. The second and third of these features indicate a relationship with the Tracheate groups; on the other hand there is an absence of paired sensory appendages, and of mouth-parts. Von Erlanger has pointed out t
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Keywords: ., boo, bookcentury1800, booksubjectzoology, bookyear1895, tardigrade
