952 SUMMARY OF CURRENT RESEARCHES RELATING TO 



to revert to a free, carnivorous life, which, starting from Pontohdclla 

 and lirancheUion, culminates in Aulostuma ami Ilsemadipsa. The most 

 parasitic forms arc all marine, emancipation from tho parasitic mode of 

 life having gone on in fresh water ; the most parasitic are by far tho 

 richest iu individuals, but very poor in species. IchthyohdcUa appears 

 to be the link between the free Annulate ancestor and the Selachian 

 parasites Pontohdclla and Branchellion. Ci/UcohdcUa leads through 

 Lumbricobdella to Nephelis, and by another line to Uirudo, and Ilsema- 

 dqisa, and to Aulostoma. Piscicola leads to Clcjjsine. Tho author 

 ftl)pcars to have examined a large number of species of Leeches, some of 

 which seem to be new, but are not here diagnosed. 



Nerve-endings in the Leecli-* — Hcrr J. F. Heymann has in- 

 vesti"ated the uerve-eudiugs in the uustriped muscle-fibres of the leech. 

 His results differ from those of previous investigators. Thus, besides 

 the ventral visceral nerve there are two quite similar in a dorsal position. 

 The main nerve-plexus lies between the circular and longitudinal sheath 

 of muscles. This is known to be connected with a peripheral or inter- 

 muscular, but what the exact endings were has been doubtful. According 

 to the author distinct terminal plates may occur on the terminal fibrils, 

 or these may be absent. Sometimes one muscle-fibre was seen to have 

 four associated terminal plates. In the lateral contractile vessels the 

 author maintains the existence of two muscle-layers, circular and longi- 

 tudinal, but formed from the same fibres. Their innervation and the 

 termination of the fibrils in ovoid knots arc described. Finally, Ilerr 

 Heymann describes how the lateral nerves from the ventral chain are 

 associated with the voluntary muscles. Each twig ends in a granular 

 plate in and not on the contractile sheath of the muscle-fibre. 



Creeping Movements of Earthworm.! — In the course of experiments 

 on earthworms Herr B. Friedlilnder was led to make some interesting 

 observations in regard to their creeping movements. If some of the 

 posterior segments of an earthworm be cut off, the animal acts quite 

 normally ; it bores at once into the earth. But if some of the anterior 

 6e<Tments be cut off, the worm begins at once to move and twist violently, 

 and creeps about for a time. It soon becomes quiet, however, and may 

 lie on damp earth for weeks without moving. On the slightest irritation 

 it awakes out of its passivity, moves or creeps about for a little, but 

 soon relapses into its former lethargy. Still more interesting is tho 

 following experiment, A ventral lateral incision was made about tho 

 middle of a worm, and a small portion of the nerve-cord removed. Herr 

 Friedlander found, to his astonishment, that worms which had been 

 so treated crept exactly like normal animals. In explanation, he dis- 

 cusses the possibility of the stimulus being transmitted directly from 

 muscle to muscle, but gives reasons against the probability of this. He 

 is inclined to believe that the pull is transmitted in a purely mechanical 

 way through the enervated region, and that the rest is reflex. He 

 supposes that " a longitudinal extension sets up a longitudinal contraction 

 as a reflex movement, and thus the locomotion of the normal and of tho 

 injured worm are explicable in one and the same way." His facts, he 

 submits, at least remain. 



• Arch. Anut. rhysiol. (Physiol. Abth.), 18S8, pp. 556-GO. 

 t Biol. Centralbl., viii. (1888) pp. 363-6. 



