634 MR. H. G. NEWTH ON THE 



many but not all of the larvae, near the equator, and at the 

 SRme time the stomodseum arises as a crescentic invagination at 

 the junction of the opaque and the less opaque regions of the 

 body (age = 48 hours). The formation of the stomodfeum pro- 

 ceeds by the extension backwards of the horns of the crescent, 

 their ultimate fusion in a posterior lip, and the in-sinking of the 

 enclosed area. From the orifice tlius established the five primary 

 oral tentacles, formed pari passu with the stomodteum, soon come 

 to project. They are tipped with little hyaline excrescences, 

 and can be entii-ely withdrawn into the stomodseum, (PL I. 

 fig. 6.) 



During the completion of the stomodaeum the primary tube- 

 feet make their appearance as two circular depressions in the 

 ectoderm ; and from this time onwards the asymmetry of the 

 larva (comparable to that of the Auricularia "pupa") is manifest. 

 The stomodjeum lies, very obviously, to the left of the median 

 ventral line as determined by the tube-feet, and of these latter 

 tlie left is placed further forward than the right. It is interesting 

 to note that Ludwig describes the right primary tube-foot of 

 C. planci as being the more anterior of the two. Fig. 6, which 

 is of the corresponding stage in C. saxicola, shows the displace- 

 ment of the stomodseum, but a less-than-average displacement 

 of the podia. 



jSTo further external change, except growth of the tentacles 

 and the tube-feet, occurs during the free-swimming life of the 

 animal. The ciliation of its surface is uniform at every stage : 

 there is no segregation of the cilia into bands as there is in the 

 larva of C. planci (Selenka, 11). On the fourth and fifth days 

 the larvae still swim near the surface, but towards the end of the 

 fifth day they tend to sink to the bottom and settle down upon 

 their oral tentacles. Beyond this stage I shall not, at present, 

 follow their development. 



Formation and Segmentation of the Coelom. 



The segmentation cavity appears during the formation of the 

 wrinkled blastula from the solid morula. It is at first empty, 

 i. e. it contains nothing that is coagulable by any of the usual 

 fixatives — and no cell-communications exist, such as are required 

 by Sedgwick's conception of the blastula as a syncytium. Mesen- 

 chyme and " blastocoel jelly" appear simultaneously later and 

 seem to be identical, the processes of the cells merging iudistin- 

 guishably, in sections, into the reticulations of the jelly, the 

 interstices of which are filled with oil droplets. Since, however, 

 this oily yolk uniformly fills the spacious blastocoel of later stages, 

 it would seem that it must be contributed in part by cells other 

 than those few which are found in it, and the fact, among others, 

 that in the blastula there occur rounded, enucleate fragments of 

 cytoplasm supports this view (fig. 5, +). 

 ' It was stated of C. planci by Ludwig, that mesenchyme and 



