258 SUMMAKY OF CURRENT RESEARCHES RELATING TO 



Annulata. 



Minute Structure of Sclerocheilus minutus.*— Aruiand and Lota 

 Dehorne have made an intimate study of this Scalibregmid Polychaet. 

 They deal with the alimentary canal, the circulation, the brain, the eyes, 

 and the nephridia. There are four masses of visual cells, and four optic 

 nerves. The ocular masses may be regarded as formed of a large number 

 of inverted ocelli of the Platyhelminth or Rhynchobdellid type. The 

 visual cells are intra-epithelial, never sub-epithelial. A detailed histo- 

 logical account is given of the eyes and the nephridia. 



Nervous System of Polychaets.f — David Nilsson has made a 

 detailed study of the nervous system and sensory structure of Am- 

 phictenidae, especially Pectinaria (Lag is) Jcoreni. The brain is three - 

 lobed. In Amphictenidse, Ampharetidae, and Terebellidas it is possible 

 to distinguish three portions like the fore-, mid-, and hind-brain of the 

 free-living forms. The oral tentacles, antennular membrane, and nuchal 

 organs of Amphictenidse are shown to be homologous with the palps, 

 antenna?, and nuchal organs of free-living forms. The lateral nerves 

 show a dorsal motor root and a ventral mixed root. There is a sub- 

 epithelial nerve plexus. Bipolar isolated sensory cells occur all over the 

 body : they form an essential part of nuchal organs and lateral organs. 

 The theory is upheld that the definitive brain of Polychseta is composed 

 of three pairs of pedal ganglia shunted forwards, and is anatomically 

 comparable to the brain of Arthropods. 



Modifiability of Leech Behaviour.:}: — Wilson Gee has made a study 

 of the behaviour of leeches, with special reference to its modifiability. 

 His observations were made on two species, Dina microstoma Moore 

 and Glossiplionia stagnalis Linn. The first part of the paper discusses 

 the general reactions of the species in question. The author finds 

 that the most significant single feature of leech behaviour is the 

 tendency to exploratory " random " movements, and that the chief 

 function of the brain in the leech appears to be the production of 

 spontaneity of movement, since decapitated specimens show a marked 

 decrease in the number of internally initiated movements. No trace 

 of a " parental instinct " could be found in the adults ; they carry 

 their young only because the small leeches are very persistently and 

 strongly thigmotactic. 



In studying modifiability of leech behaviour the investigator con- 

 siders only the modifications of reflex responses without the intervention 

 of intelligence, and attempts to analyse behaviour into its component 

 physiological factors. Contact-stimulation of the anterior end of the 

 body evokes responses varying with the intensity and localization of 

 the stimulus, the position of the body at the time, the tonus of the 

 organism, and the sequence of the reaction in the chain-reflex involved. 

 The leech readily becomes accustomed to slight shocks and shadows 



* Arch. Zool. Exper., liii. (1913) pp. 61-135 (4 pis. and 27 figs.). 



+ Zoolog. Bidrag Uppsala, i. (1911-12) pp. 85-161 (3 pis. and 12 figs.). 



X Univ. California Publications (Zool.) ii. (1913) pp. 197-305 (13 figs.). 



