ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 327 



oesophagus, but also the rnadreporic pore and the left anterior coelorne, 

 so that these come to be near the right hydrocoele. The origin of the 

 perihsernal canals is described. From their walls originate the motor 

 ganglion cells and in all probability the ventral intervertebral muscles. 

 The primitive germ-cells originate from the left posterior coelome 

 covering the stone canal, 



Monograph on Apodous Holothurians.* — Herbert Lyman Clark has 

 completed a valuable monograph on the Synaptidse and Molpadiidse. 

 It has been based on the collection of over two thousand specimens in 

 the United States National Museum, and is intended as a complete 

 account of all the apodous Holothurians known to science. The author 

 deals with structure, functions, habits, inter-relations, development, and 

 classification. Of Synaptidae there are 21 genera and 88 species ; there 

 is every reason to believe that the common ancestor was a small 10- 

 tentacled apodous form, probably with wheel-shaped calcareous particles ; 

 Rhdbdomolgus seems to be the nearest living representative of the 

 ancestral stock, though it is not necessarily close to it ; Polyplectana, 

 Protankyra, Polycheira, and Acanthotrochus are the most highly special- 

 ised forms on the four different branches on which the Synaptid genera 

 may be arranged. Of Molpadiidse there are 8 genera and 46 species ; 

 the ancestor of the group was probably a 15-tentacled pedate Cucu- 

 marian ; to this it may be that Himasthleplbora is nearest, while 

 Gephyrothuria is also primitive. The author is to be congratulated on 

 the completion of a very fine piece of work. 



Coelentera. 



New Types of Alcyonarians.f — Louis Eoule refers briefly to two 

 new types which he found in a collection from Amboina. The first is 

 Pachyclavularia erecta g. et sp. n., in which the mesoglcea of the basilar 

 membrane is so thick that the encrusting mode of growth characteristic 

 of Clavularids is replaced by one more or less erect. The second is a 

 Virgalarid — Svavopsis elegans g. et sp. n., which has no pinnules or 

 calices. 



Association of Alcyonarian and Alga. J — Ch. Gravier describes a 

 case of association in very large numbers of a unicellular alga with an 

 Alcyonarian, Sarcophytum mycetoides Grav. In the first stages the alga? 

 are regarded as parasitic, but once established and its nutrition assured, 

 the relationship becomes symbiotic. The case is regarded as parallel 

 with that of Convoluta and its green cells. 



O' 



Spines of Antipatharia.§ — Louis Roule has investigated the ques- 

 tion of the morphological significance of these structures. His con- 

 clusion is that they are abortive branches, and correspond to branches 

 of the axis. Antipatharians with undivided colonies have only these 

 abortive structures, while those that branch exhibit a normal develop- 

 ment. These conclusions have been arrived at by a comparison of 

 Antipatharians with a complete colony of a new Gorgonid genus 

 Rhopalonella, from the Antarctic seas. 



* Smithsonian Contributions to Knowledge, xxxv. (1907) 231 pp., 13 pis. 



t Comptes Rendus, cxlv. (1907) pp. 946-7. 



X Op. cit., cxliv. (1907) pp. 1462-4. § Tom. cit., pp. 1453-4. 



