ASPLANCHNAD.E. 123 



A. PEIODONTA, Gosse. 



(PI. XII. fig. 2.) 

 Asplc.nchna priodonta ' . . Gosse, Ann. Nat. Hist. 2 Ser. vol. vi. 1850, p. 18, pis. i. ii. 



SP. CH. Female without humps; eyes three; rami broadening to the free ends, 

 their inner edges- serrated; contractile vesicle about equal to the two gastric glands to- 

 gether; vibratile tags four on each side, attached to a single coil of tubes; ovary 

 roundish; male without humps. 



Mr. Dalrymple's exhaustive memoir on A. Brightwellii was followed soon afterwards 

 by a similar paper of Mr. Gosse's on his new species, A. priodonta, in which its structure 

 is described with the greatest minuteness and care. A. priodonta was discovered by 

 Mr. Gosse in the Serpentine, in Hyde Park, in 1850. It is much smaller than A. Bright- 

 wellii, its outline more oval, its head more conical. The jaws are broader : and instead 

 of a projecting tooth on the inner side, they have this edge minutely serrated, with the 

 tip forming two curved long teeth (figs. 2/, 2</). Each carries a spine proceeding from 

 its back and curving round nearly parallel to its extremity. The gastric glands are 

 situated on the oesophagus itself, a little above the stomach, not 011 it. But the chief 

 differences lie in the vascular and reproductive systems. The contractile vesicle, when 

 full, is globular and small, being scarcely, if at all, bigger than the two gastric glands 

 together. The fiocculent ribbons that support the lateral canals have their middle parts 

 wrinkled into a large coil of four or five pairs of doublings, and on this coil are placed 

 four vibratile tags ; so that there are only eight tags in all. The ovary is roundish and 

 very small ; it is shown in fig. 2a with its germs, and the ovisac wrinkled up close to it. 

 In fig. 2 it is behind and above the ovisac, which contains a developing ovum with 

 salmon-coloured oil-globules in it. There are three crimson eyes (fig. 26), one under 

 the centre of the corona and one on each side of it ; each resting 011 a nervous ganglion. 



The male (fig. 2c) differs hardly at all in its internal structure from that of A. Ebbes- 

 bornii, though very different in shape. Its sperm-sac is supported by a strip of tissue 

 that hangs from the head, and resembles in shape and position the alimentary canal of 

 the female. It is, however, imperforate and structureless, and seems to have no other 

 office than to support the sperm-sac and penis. The nervous ganglion (fig. 2cZ) is un- 

 usually conspicuous. Two of its four diverging threads pass downwards to the dorso- 

 lateral rocket-headed antennae (figs. 2c, 2e), and two pass upwards to similar antennae 

 on the two apices of the corona. 



By slightly compressing a male, I put beyond question the fact that the contractile 

 vesicle empties itself outward through the cloaca ; for under slight pressure the vesicle 

 contracted slowly, by stages as it were, collapsing partially in separate efforts instead of 

 closing at once. As it did so, I distinctly saw, at each effort, the gradual passage of a 

 plug of fluid down the cloaca, dilating its walls as it went. 



Length. Female, ^ inch ; male, -fa inch. Habitat. Kensington Gardens, Serpentine 

 (P.H.G.) ; ponds and ditches round Clifton and Birmingham (C.T.H. ; T.B.) : not un- 

 common. 



1 Ehrenberg's Notommata syrinx is wonderfully like A. priodonta, but is said to have a cloaca, and 

 a minute foot and toes. His N. myrmeleo is unknown in England, but Leydig has made it clear 

 (Ueb. d. Bau. d. Raderth. p. 20, Taf. iv. fig. 36) that in this instance Ehrenberg has made a mistake, 

 and that the Eotifcron has not got the cloaca which Ehrenberg describes. It is therefore an Asplanclma 

 with a foot ; one much resembling that of Notops clavulata. Its jaws, ovary, vascular system and eye 

 resemble those of A. Brigliticellii. 



Leydig (loc. cit.) has described another Notommata, N. Sicboldii, which is a true Asplanchna. The 

 female closely resembles A. Brightwellii ; but the male, which is conical in shape, has four humps, 

 two lateral ones and two on the neck, just like those of the male of A. Ebbenbornii. 



