ZOOLOGY AND BOTANY, MICEOSCOPY, ETC. 163 



Origin of Ascidian Mouth.*— A. Gr. Huntsman has studied this in 

 Chwelina, Dendrodoa (Siyelopsis), and Gsesira (Molgnla), and has reached 

 the unexpected result that a large part of the epithelium of the wall of 

 the oral cavity is derived from the primitive neural tube of the embryo. 



New Type of Compound Ascidian. f — A. Oka describes a remark- 

 able compound Ascidian from Japan, Gyathocormus mirabilis sp. n., for 

 which a new family will be required. The colony is fixed and stalked ; 

 the portion composed of zooids is like a beautiful open cup. The mouth 

 of the cup is the common cloacal opening, the cavity of the cup the 

 common cloaca. The wall of the cup consists of a single layer of 

 zooids, with their anterior ends external and their posterior ends 

 internal. The body of each is divided into a thorax and an abdomen, 

 the latter with a long vascular appendage. The peribronchial wall is 

 imperfectly developed ; the stigmata of the branchial sac open directly 

 into the central common cloaca. 



The test is soft, gelatinous, and transparent ; there are no calcareous 

 spicules ; the bladder-cells are very numerous. There are four rows of 

 stigmata on the well-developed branchial sac. No internal longitudinal 

 vessels are present. The stigmata are very long and narrow. The 

 tentacles are simple. The dorsal lamina is represented by a series of 

 languets. The gut forms a simple loop posteriorly to the branchial sac 

 The gonads are not conspicuous. An incubatory pouch is present. 

 There is a tailed larva. 



Oka considers this interesting form as representative of a new 

 family, somewhere in the neighbourhood of Distomidas, e.g. near Golella, 

 but leading in the direction of Pyrosoniidae. In many ways it agrees 

 with Pyrosoma and serves to link that type nearer to other Ascidise 

 cornpositae. 



INVERTEBRATA. 



Mollusca. 



5. Lamellibranchiata. 



Development of Anadonta cellensis.J — Karl Herbers has reared 

 the young stages artificially to a length of 3 '13 mm. ; from 5" 7 mm. 

 in length onwards the stages were found in natural conditions. The 

 primary mesoblasts form two bilaterally symmetrical mesoderm-bands, 

 which can be traced into the glochidium, and do not break up into 

 loose mesenchyme. The young shell of Anodonta differs in shape and 

 colour from that of the adult ; it has a typical wavy sculpture, and 

 carries the glochidial shell for a considerable time. The labial palps 

 arise from two epithelial folds ; the gills from rows of papillae. 



A saccular invagination, homologous with a byssus cavity, arises 

 from the pedal epithelium and moves inwards to near the pedal ganglion. 

 Besides the paired statocysts, there are the osphradia and the adoral 



* Proc. Roy. Soc, Series B, lxxxvi. (1913) pp. 454-9 (2 figs.). 



t Journ. Coll. Sci. Univ. Tokyo, xxxii. (1913) Art. 12, pp. 1-30 (3 pis.). 



t Zeitschr, wiss. Zool., cviii. (1913) pp. 1-174 (104 figs.). 



