ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 607 



tlieir ends, and sliglitly swollen in the middle. Twelve pinnate ten- 

 tacles were so distributed as to lie, three for each of the lateral dorsal 

 interradii, and two for each of the other interradii. The calcareous 

 ring consists of three joints, and into the radial pieces there are 

 inserted five short retractor muscles. 



The genital tubes ajDpear to give rise to both ova and sperma- 

 tozoa, the latter being developed in their blind ends and lateral 

 branches. 



Lying freely in the coelom there were sixteen young, all at about 

 the same stage in development ; the body- wall was so transparent that 

 the intestine could be seen. There were five tentacles at the anterior 

 end, each of which had two small depressions (the future pinnate 

 lobules) at its tip. In the body-wall there are to be seen groups of 

 developing or developed calcareous wheels, which at first have the form 

 of a six-rayed star, each ray of which has at its free end a process on 

 either side ; later on the two neighbouring processes unite and so form 

 the circumference of the wheel. 



For fui'ther investigation, the specimens were either clarified as a 

 whole or cut into sections. It was then seen that, in addition to the 

 five tentacles 3 mm. in length, there were two others 1 mm. long, and 

 that these lay more internally. The five larger ones appear to double, 

 and so the somewhat remarkable number of twelve is arrived at. No 

 circular, but only longitudinal muscular fibres could be made out in 

 the walls of the tentacles. A small rounded Polian vesicle depended 

 ventrally from the water-vascular ring, and dorsally there arose the 

 interesting stone-canal, which takes a curved course to the body- 

 wall. 



Here it is continuous with a backwardly directed canal which 

 extends throughout the whole length of the body, and lies between 

 the ectodermal and endodermal layers. This canal ends in a blind 

 terminal piece. It is well known that in most cases the stone-canal 

 loses, in the adult Holothurian, all connection with the exterior, 

 although in some cases, as Keren and Danielssen have lately shown, 

 there is such a connection throughout the whole life. Dr. Ludwig 

 looks upon the arrangement here described as being an intermediate 

 stage. 



The nerve-ring and its radial nerves consist of an outer cellular 

 and an inner fibrous ring ; outside the nerve-ring there is a special 

 cavity, which becomes considerably enlarged between the tentacles, 

 and contains mesoderm-cell-like elements. This may be a rem- 

 nant of the cleavage cavity. Small vesicles are found by pairs in 

 connection with each of the radial nerves, and are regarded by the 

 author as comparable to the so-called auditory vesicles of other 

 Synaptids. 



The paper concludes with the description of two new species from 

 Brazil — Thyonidium parvum and Synapta Benedeni ; the latter has the 

 general appearance of S. digitata, but in the form of its anchoring 

 spicules it seems to come nearer to S. pseudodigitata. 



