612 SUMMARY OF CIJKKENT RKSEARCHKS RELATING TO 



8. Arachnida. 



New Myriopodophilous Mite.* — Ivar Tragardh describes Disco- 

 meg istus pectinatus g. et sp. n., found on Rhombocephalus gigantea in 

 Trinidad. The body is flat, transversely oval ; the dorsal shield is 

 surrounded by a marginal shield which bears a dense row of fusiform 

 setae. It seems likely that Discomegistus and Discozercon Berlese belong 

 to a group which has branched off from the more primitive ancestors of 

 the modern Anteunophorin^, and instead of developing the ambulacra 

 into large suckers has acquired a special organ for adhesion, namely, a 

 modified metapodial shield. 



Haller's Organ in Argas.f — Edward Hindle and Clordon Merriman 

 have studied the sense-organs and sensory perceptions in Argas persicus 

 (Oken). All show an olfactory sense. Haller's organ, situated at the 

 end of the first pair of legs, is olfactory in function, and enables the tick 

 to recognize its host. When deprived of this organ, ticks will feed on. 

 other media than blood, thus showing that the sense of taste has dis- 

 appeared. All stages of A. persicus are negatively phototropic. They 

 always select the darker places. In the gorged state the ticks are to a 

 slight degree positively geotiopic, but not in the unfed state. In all 

 stages the tick tries to bring as much of its surface as possible into 

 contact with its surroundings. There is a distinct attraction to warmth. 



Tardigrades of Sweden. | — Gustav Thulin describes a new species of 

 Echiniscus, a new genus Pseudechiniscus, several new species of Hypsihius, 

 and a new species of Macrobiotus ; and reports on 40 species altogether. 



«• Crustacea. 



Sensory Cells in End Gut of Crayfish. § — Fr. J. Rainer has demon- 

 strated by the intra-vitam methylen-blue method the presence of sub- 

 epitheUal bipolar nerve-cells in the mucosa of the hind-gut. The 

 peripheral prolongation of one of these cells passes between two epithelial 

 cells to the cuticle. The central prolongation never divides ; it was 

 frequently seen to unite with the longitudinal nerves of the intestine, 

 which consist especially of motor fibres. Besides these cells the blue 

 showed a certain number of Leydig's cells (which recalled the appearance 

 of multipolar nerve-cells) and of terminal arborizations on the longitudinal 

 muscle-fibres. There seems no doubt as to the reality of intra-visceral 

 sensory neurones. 



Larvae of Passiphaea. || — W. Bjorck describes the planktonic larvae 

 of Passiphsea tarda which leaves the large eggs at an advanced stage — 

 more advanced than is the case with Hippolyte polaris and Sabinea 



* Arkiv f. Zool., vii. (1911) No. 12, pp. 1-21 (13 figs.). 



+ Parasitology, v. (1912) pp. 203-16 (2 figs.). 



X Arkiv f. Zool., vii. (1911) No. 16, pp. 1-60 (31 figs.). 



§ C.R. Soc. Biol. Paris, Ixxiii. (1912) pp. 350-1. 



'll Arkiv f. Zool., vii. (1911) No. 15, pp. 1-17 (1 pi.). 



