120 MR. H. CHARLTON BASTIAN'S MONOGRAPH 



such as glycerine, almost immediately shrivel up, owing to the rapid osmosis of fluids 

 from Avithiu ; or, when placed in a colouring solution of magenta, the whole of their 

 tissues become S2)eedily and uniformly dyed of the same hue. But if a species of either 

 of these four land and freshwater genera be submitted to the same conditions, they 

 exhibit totally diiferent results : they will continue to move about in glycerine for about 

 fifteen or twenty minutes before commencing to shrivel, and will remain nearly as long 

 in a strong magenta solution with the body uncoloured, save for a very short distance 

 from the mouth and anus. Both these experiments seem to indicate that there is not 

 such a free communication through the integument, in these species, between the in- 

 ternal parts of the l^ody and the external medium, and that the integument is hermeti- 

 cally sealed, excepting at such natural apertures as mouth, anus, and vulva. This 

 property may be one of the factors concerned in producing the extraordinary tenacity of 

 life observed in these animals, — one of small significance, however, when we attempt 

 to explain the very prolonged periods of suspended animation, extending over a series of 

 years. This power of remaining for lengthened periods to all intents and purposes 

 dead, inasmuch as thei-e is a negation of all that we are apt to consider as the charac- 

 teristic attributes of life, save that, like seeds, they still retain the potentiality of re- 

 suming their vital manifestations under the influence of suitable external conditions, 

 must, doubtless, depend upon inherent peculiarities of the tissues themselves, beyond 

 the reach of detection by optical instruments even of the highest power. 



Another peculiarity of these four genera is the fact that they all possess the excretory 

 gland in a modified condition, though I have not met with it at all in any of the other 

 land and and freshwater types. 



1. T. Davainii, n. sp. (Plate X. figs. 109-111.) 

 Female, length -^", breadth yto"' 



External Characters. — Body tapering at both extremities, especially towards posterior. 

 Head narrowed, truncate. Integument thick ; striae transverse, distinct, j-sVo" apart. 



Spear large, t^^s" long. (Eso2:)hagi(s |th of total length ; posterior part, behind median 

 swelling, gradually widening. Intestine not very distinct from body generally, being 

 obscured by large, coarse, colourless granules. Anus -jgu" from posterior extremity. 

 Vulva considerably behind middle of body, -/o" from anterior extremity. Excretory 

 duct distinct, opening opposite posterior part of oesophagus, and extending backwards 

 for about -g^", where it terminates in an ovoid sac. 



Mule, same size as female. 



(Esophagus shorter. Anns ^\^" from posterior extremity. Spicules rather narrow, 

 ■fxi" long ; accessory piiece of about half this length. AUb transparent, narrow, ex- 

 tending, on either side, from slightly above to a little below the anus. 



Hah. From sheet of moss covering large boulder lying in a freshwater stream, Fal- 

 mouth. 



2. T. TiuciTi. (Plate X. figs. 112-111.) 

 Needham, Micr. 99, tab. v. 7. 



Baker, Micr. Expl. SO, tab. v. fig. 9. 1, 2. 

 Koffredi, in Journal de Phys. 1775, p. 369. 



