546 SUMMARY OF CURRENT RESEARCHES RELATING TO 



also given of the minute structure of the food-canal. The author gives 

 a key to all the species of Thalassema, and establishes the new genus 

 Ikeda for Ikeda taeniodes (Ikeda), a Gephyrean of unusually large size 

 (body 40 cm. ; proboscis 150 cm.), in which the nephridia are indefinite 

 in number (200-400), not arranged in pairs, and are provided with 

 terminal funnels. The longitudinal muscle of the dermal muscle layer 

 lies on the outside of the circular and oblique layers, not between them 

 as in Thalassema. 



Echinoderma. 



Minute Structure of Mesothuria intestinalis.* — W. Haanen gives 

 a full account of the structure of this Holothurian, common in northern 

 seas and in the Mediterranean. He deals with the calcareous bodies in 

 the skin ; the cuticle, epidermis, cutis, transverse musculature, longi- 

 tudinal musculature, and ccelomic epithelium ; the blood-cells and non- 

 granular plasma cells, the granular plasma cells, the free excretory cells, 

 and the phagocytes in the gonads. 



In connexion with the water-vascular system, Haanen describes the 

 annular canal, the single polian vesicle, the tentacular and radial canals, 

 the ampullae, and the stone canal. A full account is given of the 

 annular nerve, the radial nerve, the oesophageal nerve, and the innerva- 

 tion of tentacles, tube-feet, and skin. A radial section shows from 

 within- outwards, the longitudinal muscle, the radial water-vessel, the 

 radial blood lacuna, the hyponeural canal, the inner and the outer nerve- 

 strands separated by a partition, the epineural canal, connective-tissue, 

 and the epidermis. 



The minute structure of the different areas of the alimentary canal 

 is described. There is no convincing evidence that migratory cells are 

 formed in the wall of the respiratory trees. These trees have the same 

 minute structure as the intestine — ciliated ccelomic epithelium, longi- 

 tudinal muscles, a sparse matrix of connective-tissue, circular muscles, 

 internal connective-tissue, and an internal epithelium of cube-shaped 

 cells. The mesenteries, the various sinuses, and the vascular system — 

 annular, radial, podial, intestinal, and genital — are described. There are 

 no Cuvierian organs. The systematic position of Mesothuria is discussed. 



Musculature and Skin of Holothurians.t — H. Jordan divides 

 Metazoa into two groups according to their mode of locomotion. On 

 the one hand there are " lever animals," such as Vertebrates and 

 Arthropods which have lever-like appendages moved by flexors and 

 extensors. On the other hand, there are bladder-like animals (hohlor- 

 ganartige or reflexarme), without skeleton, with a wall of smooth muscle 

 fibres (annular and longitudinal). The turgor of the internal fluid takes 

 the place of a firm skeleton. As examples, Gastropods, Lamellibranchs, 

 Ascidians, and Holothurians may be mentioned. 



The first main conclusion of Jordan's experimental investigation is 

 that the musculature of Holothurians does not behave as that of a 



* Zeitschr. wiss. Zool., cix. (1914) pp. 185-255 (2 pis. and 2 figs.), 

 t Zool. Jahrb. Abth. Allg. Zool., xxxiv. (1914) pp. 365-436 (9 figs.). 



