296 Dr. F. Leydig on Hydatina senta. 



living in the stomach of the female Hydatina, which appears to 

 be hitherto undescribed, and may be referred to Ehrenb erg's 

 family of the Astasisea. The parasite was so plentiful, that nearly 

 every Hydatina, out of hundreds that were examined, had at least 

 one in its interior ; nay, it was found that very young individuals, 

 of which the stomach was still colourless, harboured as many as 

 five or six of these creatures. If it should be supposed that it 

 might be a pseudo-parasite, which forms some part of the 

 nourishment received, an idea which may occur at first, this 

 is contradicted by the fact that the animalcule is never met with 

 in a condition which indicates, even to a certain extent, that, 

 like other swallowed animals, such as Euglence, it is subject to 

 the digestive power of the stomach ; it is rather found always 

 uninjured, and in most powerful movement. 



Our animalcule (PL VIII. fig. 6) is of the size of Euglena viridis, 

 and has considerable resemblance to it in form ; but it appears 

 to be most nearly allied to the Distigma tenax of Ehrenberg 

 [Proteus tenax of Miiller and Schrank). The foundation of its 

 body is formed by a soft, gelatinous substance, from which 

 no proper cortical layer or skin has separated. In the interior 

 there are numerous globules, of a fatty lustre, of various sizes, 

 and not of a simple round form, but which appear sometimes 

 stratified, sometimes as if pierced by an orifice, and sometimes 

 repeatedly divided; many look as if they had undergone seg- 

 mentation into four portions. After pressure with the glass 

 cover, they acquire a tolerably intense indigo-blue colour. In 

 consequence of these bodies, which resemble fat-drops, the para- 

 site appears very white by reflected light. Moreover, towards 

 the anterior extremity of the body, two clear, nucleus-like bodies 

 are distinguished, and these again display a more opake spot. 

 Lastly, a reddish point, or " eye-spot,'^ which has a sharply cir- 

 cumscribed form, is situated quite in front. The movements of 

 the animal are very lively, especially when the stomach of the 

 Hydatina begins to make unusual contractions on the occurrence 

 of any deficiency of water ; it then endeavours to escape from 

 the intestine, and if it succeed in this, it hurries away there- 

 from in great haste by its peristaltic contractions. The animal- 

 cule swells up, and constricts itself from before backwards, in 

 a manner analogous to that in which, in the contractions of the 

 muscles of the lower animals, a thickened space is often seen to 

 pass in an undulating manner along the muscle. 



EXPLANATION OF PLATE VIII. 



[All the figures magnified about 300 diameters.] 



Fig. 1. The head of the female Hydatina from below, to show the form of 

 the rotatory organ : a, the pharynx, should be represented further 

 forward nearer to the buccal orifice; 6, b, muscles. 



