INTRODUCTION. 5 



animal, very suitable for the purpose of description, and one which bears the tem- 

 porary captivity of a compressorium remarkably well. 



The Female. 



Fig. 1, PI. A, represents the dorsal aspect of the female of this Brachionus, and 

 fig. 2 the upper part of the ventral aspect. The drawings are from life ; but the out- 

 lines of the various organs have been made unnaturally sharp and distinct, for the sake 

 of clearness. The dorsal and ventral surfaces may be distinguished from each other in 

 the great majority of the Eotifera by the following considerations : 



First, as to the dorsal surface : 



(1) It is arched (fig. 5). 



(2) The stomach (fig. 1, s) passes down it ; between it and the ovary (fig. 1, ay). 



(3) The cloaca (fig. 1, cl) is on it ; in the median line. 



(4) There is almost invariably one antenna (fig. 1, a) (or a coalesced pair) on it ; placed 

 anteriorly on the median line. 



(5) The eye or eyes (fig. 1, e) are towards the dorsal surface. 



(6) In swimming over objects the Eotiferon keeps the dorsal side upwards. 

 Secondly, as to the ventral surface (fig. 2) : 



(1) It is comparatively flat. 



(2) The entrance to the mouth hes on it (figs. 2, 5, bf), 



(3) The ovary is placed close to it (tig. 2, 5, oy). 



In the case of those Eotifera whose dorsal and ventral surfaces have much the 

 same contour, the above considerations present points of difference enough to decide 

 between the two.' 



B. rubens is inclosed in a case or lorica (figs. 3, 4, 5) which is both hard and trans- 

 parent. The internal structure can be readily seen through it ; and, by suffering the 

 animal to dry on a glass slip, and then dropping on it a solution of caustic potash, the 

 softer portions of the body may be dissolved away, and the lorica left unharmed. 



It will then be seen to be closed above and below, with an opening at each end, like 

 the shell of a tortoise. From the front opening the head is protruded, and from the 

 hind the psetidopodium or foot (fig. 1,/). 



The lorica has a glassy shining surface, and is armed with six short sharp spines in 

 front, of which the central pair is the longest. Four of them are distinctly on the dorsal 

 surface ; but the outmost pair belongs as it were to both surfaces, being on the edge 

 where they meet. 



The front edge of the ventral surface (the mental edge as it is sometimes termed) ^ 

 is hollowed out symmetrically into graceful curves (fig. 4). 



The lorica widens from the front backwards, till, at about two-thirds of its length, it 

 reaches its maximum breadth ; and is then rounded off by two ogee curves that are 

 separated, by a square notch on the dorsal surface, but by a nearly circular one on the 

 ventral. In consequence, it is often said that the lorica has two blunt spines behind 

 on the dorsal surface ; but this is somewhat misleading, as these so-called spines are 

 merely the sides of the excavation. Strong ridges from each of the four central front 

 spines run down about one-third of the dorsal surface (fig. 3), and still longer ridges 

 mark the ventral surface with sweeping curves (fig. 4). 



The median portion of the lorica is by far the deepest, and in it the internal organs 

 mainly lie. The dorsal surface of the lorica slopes upwards from the head to its line of 

 greatest width (fig. 5), and then abruptly falls to meet the under surface ; the whole lorica 

 thinning off there mto closely approaching plates, through the excavation in which the foot 

 can pass. Each side, too, of the median portion of the lorica thins off in a similar 

 manner ; so that the dorsal and ventral surfaces meet everywhere (except at the head) in 

 a shai-p edge. 



' Cf. Dr. Moxon, Trans. Linn. Soc. vol. xxiv. 18G4, p. 455. ^ From mcntum, the chin. 



