On the Anatomy of LeiAodora hyalina. By H. E. Forrest. 829 



of which it is attached by slender hgaments of connective tissue. 

 Fig. 12 is a dorsal view of the heart showing the arrangement of 

 the muscles. It pulsates very rapidly, pumping the blood along 

 just like a pair of bellows. Leptodora cannot be said to have any 

 true arteries or veins, the blood merely courses along the interstices 

 between the organs of the body. The corpuscles are amcsboid, 

 colourless, nucleated, and remarkably few and far between. At 

 each contraction of the heart the blood is driven forward through 

 an opening at the end nearest the head, where there is a valve 

 which prevents its return when the heart re-expands. The blood 

 then enters at the opposite end, to be in its turn driven forward, 

 and so on ad Jibitum. It is very remarkable that Leptodora 

 hyalina has no organs set apart for respiration. In the other 

 Cladocera we always find some of the limbs flattened and otherwise 

 modified so as to serve the purpose of gills, but in Leptodora the 

 whole body wall is so thin, and consequently the whole body so 

 thoroughly exposed to the oxygenizing influences of the water, 

 that the specialization of any parts for breathing organs is 

 unnecessary. 



III. Nervous System and Sensory Organs. 



The nervous system is more highly developed than might be 

 expected from the otherwise low organization of the animal. It 

 shows a degree of concentration almost equal to that of the spider 

 crabs (Maia). There is a large brain mass or cerebrum in the front 

 part of the head, and the eye rests immediately upon it (Fig. 1 , a 

 and h). The cerebrum is indistinctly divided into three parts. Two 

 upper right and left parts (Fig. 11, e and /), and one basal part 

 (Fig. 11, j), probably the remains of three ganglia which have 

 coalesced. The basal part gives off a large nerve (y) to each of 

 the two antennules. Each nerve gives off branches to the setae 

 with which these organs are studded, and it is remarkable 

 that they differ materially from the setae found on other parts 

 of the body, being truncate instead of pointed (Fig. 8, male ; 9, 

 female). Hence the end of each nerve is exposed almost naked 

 to the water, making the antennules most delicate sensory organs. 



What their precise function is, is a moot point, some authors 

 say they are for hearing, others for smelling. Sir John Lubbock in 

 his recent paper read before the British Association fully discusses 

 this question, and concludes that the latter is the most probable, 

 because the antennules are much more developed in the males than 

 in the females. If one sex attracts the other by sound, both sexes 

 would have the ear developed, for the attracted sex must be able to 

 distinguish the sound, and the singing sex must have a good ear 



