GIGANTOCYPRIS MOLLERI 203 



It is through this system that the limbs are moved relative to the ventral framework. 

 I described this briefly in Doloria levis (193 1, p. 441), but in Gigantocypris, by using 

 chlorazol black, I have been able to study the associated musculature and have deduced 

 the manner in which this sclerite system functions. The central point of the system is 

 a structure that I call the lateral brace, the position of which can be understood only in 

 relation to the attachment of body to valves. This attachment is naturally bounded by 

 a margin where the ectoderm of the body is reflected on itself and continues as the inner 

 lining of the valves. It extends downwards from the dorsal region of the heart as an 

 isthmus, and just below the equatorial region enlarges as a circular peninsula which 

 surrounds the attachment of the adductor muscle (Figs. 4, 5). The two margins, anterior 

 and posterior, of the isthmus are connected together throughout their length by a sheet of 

 attenuated cells, probably of ectodermal origin (Plate XLII, figs. 5-9). But at the lower 

 end of the isthmus there is a powerful strut, the lateral brace, which connects the two 

 margins (Figs. 4, 5 and Plate XLII, figs. 5, 6). I have not called this a tendon because 

 it does not serve as the attachment of a muscle to a skeletal part. On the other hand, 

 it is not entirely apodemal. The hinder three-quarters is a true ectodermal intucking, 

 that is, an apodeme, and this persists like the rest of the exoskeleton after treatment 

 with potash (Fig. 4). The anterior quarter, however, while not being muscular, yet 

 dissolves in potash (Fig. 5); it is endosternal in nature, like the adductor tendon, and 

 not endophragmal like the true apodemes. Despite this double nature it functions as 

 a single inextensible brace, and from its position it will be seen that it occupies a key 

 position rigidly connecting the anterior and posterior parts of the body. 



From its anterior end there extends upwards a thin skeletal rod, which is the hinder 

 member of a tripod (Figs. 3-5). This corresponds to the sclerite which I have called a 

 in Doloria. From near its upper end the outer member of the tripod articulates as 

 sclerite d, extending downward behind and to the outer side of the massive basal joint 

 of the antenna (Figs. 3, 4). It then continues upwards for a certain distance to the 

 apex of the tripod, which is situated just behind the stalk of the rudimentary paired 

 eye (Fig. 3), and then sharply downwards again. In Doloria I distinguished two separate 

 sclerites here, the upward extension b and the downward branch c. In Gigantocypris 

 I cannot find any separation, either between these or between b and a. Hence, I am 

 referring to this inverted V-shaped sclerite as abc, and the single letters refer to the 

 separate regions I have described. 



The lower end of c divides into three unequal sclerites. A very thin outer branch 

 runs laterally to support the inner side of the attachment of the antenna to the body 

 (Fig. 3). A middle branch runs downwards and is continuous with the median side of the 

 intucking which becomes the antenno-labral apodeme (Fig. 3). An inner massive branch 

 runs to the articulation of the antennules to the body, and as these articulate close together 

 in the middle line in an area of relatively rigid chitin, these inner branches of c sclerite 

 are, in effect, joined rigidly together (Fig. 3). 



The ventral framework is thus connected by a skeletal system running upwards past 

 the antenno-labral apodeme through the abc sclerite and down to the lateral brace. At 



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