308 H. JAMES-CLARK ON THE AFFINITIES OF SPONGES. 



The contractile vesicle (figs. 2, 3, 4, cv) is a much larger and far more active organ than that 

 of Anthophysa (figs. 47, 48, cv). If we view the body from its narrower aspect (fig. 2), when 

 it stands so that the lip (Ip) is nearest the eye, the contractile vesicle {cv) appears in profile, 

 on the left broad side, and so close to the surface that it seems to project beyond the gen- 

 eral outline of the body. It lies in the anterior third of the broad side just mentioned, and 

 close to the transverse plane which separates that part which contains it from the one upon 

 which the lip is placed. From whichever direction, therefore, one views this organ, it will be 

 seen to stand in an asymmetrical relation to the rest ; and as it is preeminently a dominant 

 feature, it may serve, perhaps better than any other, as a starting-point in determining the 

 obliquity of the type of this infusorian, and its perfect consonance in this respect with that 

 of the more obviously spiral forms, such, for instance, as are exemplified by Dysteria (figs. 77, 

 78) and Pleuronema (figs. 75, 76). It is so large and conspicuous that its globular form may 

 be readily seen, even through the greatest diameter of the body ; and contracts so vigor- 

 ously and abruptly, at the rate of six times a minute, that there seems to be a quite sensible 

 shock over that side of the body in which it is imbedded. 



The reproductive organ may possibly be represented by the very conspicuous, brio-ht, 

 highly refracting, colorless, oil-like globule {n), which is inclosed in a clear vesicle, and ap- 

 pears to be so constantly present in the depths of the posterior third of the body. Its posi- 

 tion seems to be invariably on that side of the transverse axial plane which is opposite to 

 that in which the contractile vesicle {cv) lies. Nothing further of a positive nature can be 

 said in regard to this body, but we may conjecture that, inasmuch as it cannot well be as- 

 signed to any other office, — not even to that of an eye-spot, — it is in all probability an 

 organ of reproduction. 



In regard to the stem (fig. S,pd), it may be added that although it appears to be of the 

 simplest nature, a mere gossamer thread as it were, it is none the less positive, as a support, 

 than that of Anthophysa (figs. 47, 48, 49, pd), and must indeed possess a similar self-reliant 

 power in order to keep the body in the same relative position in regard to the object to 

 which it is attached, or to sustain it in an upright attitude at a time when the flao-elluni is 

 quiet, and there is consequently no other means of preventing the animal from sinking 

 down upon the nearest fixed point. 



§ 2. MONAS NEGLECTA, nOV. Sp. 



(Plate IX., figs. 5, 5 a , 5 b , 6.) 



To a casual observer this species would appear to be one of the varieties of Monas termo 

 of § 1, and I must confess that under an amplification of only five hundred diameters the 

 mistake would be easily made, unless one had become perfectly familiar with the two by 

 prolonged study with a much higher magnifying power. There is, though, a physiological 

 difference which can be observed when all others could scarcely be noted, which is this : 

 the rate of the systole of the contractile vesicle {cv) of this species is double that of Monas 

 termo. Like the latter it enjoys two diverse conditions of life, namely, a fixed (figs. 5, 5 a , 

 6) and a free (fig. 5 b ) state ; frequents the same habitat; progresses with the same means' 

 and mode of locomotion, and obtains its food by similar prehensile organs, and swallows it 

 in the same manner. 



The form of the body is that of an oval, but terminates anteriorly in an obliquely trun- 

 cate front ; or rather one side of the front projects in the form of a low, rounded promi- 



