524 SUMMARY OF CUllRENT RESEARCHES RELATING TO 



time found last year in British Seas. Its discoverer was Mr. Weldon, 

 who was working at the Plymouth Laboratory. 



The smallest larvse were • 33 mm. in length, and it would seem that 

 the posterior division of the gut is not a proctodosum, but that the 

 blastopore persists as the anus without being pushed further inwards by 

 a secondary invagination of ectoderm. In later stages all the characters 

 of a Tornaria were found exhibited. The anterior body, which is pro- 

 bably formed from the amoeboid cells found in the earlier larva, is 

 connected by a muscular thread with the now conspicuous apical sense- 

 organ. A perfect Tornaria was as much as a millimetre in length, but 

 individuals vary greatly in this respect. Each ciliated cell is long and 

 columnar, slightly contracted in the middle of its length, and has a 

 large nucleus ; the cilia can be traced as fine fibrillse inwards as far as 

 the nucleus, but t'he author was unable to determine whether or no 

 they entered it. The " heart," as some authors call it, appears as a 

 vesicle lying just above and to one side of the proboscis pore. 



The central portion of the apical sense-organ is composed of columnar 

 sense-cells bearing cilia ; on it there are larger cells surrounding 

 a pair of deeply pigmented pits — the eye-spots of previous authors. 

 Beneath the sensory cells is a thin layer of nerve -fibres. 



Specimens of the larvse at later stages were never found, and it is 

 very probable that Tornaria ceases to lead a pelagic life, sinks to the 

 bottom, and undergoes its further development there. 



Echinodermata. 



Ludwig's Echinodermata.* — Prof. H. Ludwig has issued another 

 part of his work ; the description of the calcareous bodies is continued 

 and completed. The general ground-form of these bodies is, in the 

 Dendrochirota, derived from an X-shaped rudiment, which has been 

 developed by the forking of the ends of a short rod. The same is true 

 of the " stools " of the Aspidochirota, and the four-armed calcareous 

 bodies of the Elasipoda and some Aspidochirota, as well as of the 

 fenestrated plates of the Molpadidse, and the anchor-plates of the 

 Synaptidae. The anchors of these last may be referable to the same 

 scheme, but the " wheels " are more difficult to explain. Another kind 

 of calcareous body which is difficult to explain are the " tables " of the 

 Aspidochirota, which are symmetrically perforated, though there can be 

 little doubt but that they will be found to be derived from the bifurcating 

 rod. The angle at which this forking takes place is, as a rule, 120 degrees. 

 The concentrically striated bodies which are found in Trocliostoma and 

 Anhjroderma appear to be special bodies, agreeing only with the rest in 

 that they consist of an inorganic substance. 



The musculature of the bi dy-wall and the histological characters of 

 muscle are next considered. In dealing with the nervous system Prof. 

 Ludwig gives a diagram to show the relations of the parts. The central 

 nervous system consists of a circular and of radial nerves. The peri- 

 pheral nerves derived from the former of these are the tentacular, the 

 integumentary nerves of the oral disc, and that of the pharynx ; with the 

 last the plexus on the stomach and on the small intestine may be con- 

 nected. The peripheral nerves derived from the radial are those of the 



* Bronn's Klassen u. Ordnungen, ii. 3. Efhinodermata, by Dr. H. Ludwig, 

 Leipzig and Heidelberg, 1889, pp. 49-80 (pis. 1-5). 



