(j HJALMAR T1IEEL, NOTES ON TllE DEVELOPMENT OF ECHINOCARDUM AND PARECH1NUS. 



or anioebocytes. Of these latter, again, therc were two varieties, of which the first 

 were obviously stellate in form and connected with each other and the walls of the 

 Uastocoele b}' long processes. This kind of cells has been seen and figured by 

 Théel, J who, however, regarded the union of the processes of these stellate cells 

 as a secundary phenomenon.» 



The second kind of wandering cells is rounded in form, and is in fact preci- 

 sely similar to the Amoebocyte familiar to all who have studied Echinoderm anatomy. 

 I( has always been described and figured as if they were perfectly free: yet if one 

 examines a sligtly compressed living gastrula of Echinus esculentus one observes that 

 the rounded cells, which at first sight look as if they were completely free, are in 

 every ease connected either with neighbouring cells or with the walls of the blasto- 

 coele by excessively fine threads along which they apparently travel. » 



I have never been able to observe anything to confirm the account given by 

 Mac Bride. 



Those amoeboid cells, on the other hand, which play the leading part in the 

 formation and absorption of the larval skeleton, do certainly operate in a somewhat 

 different manncr, their pseudopodial conncctions and fusions beiug more intimate and 

 inore eonstant. Besides, there does not seem to exist any essential structural diffe- 

 rence between the calciferous and absorbent cells; at least, I for my own part have 

 never been able to discover any distinguishing character between thcm. In 

 1894 2 I accordingly wrote: >The cells which effect the absorption and destruction of 

 the larval skeleton are hardly to be distinguished from those which deposit unor- 

 ganic substances, and they may presumably be cousidcred to have their origin in 

 the latter. Like those they are unprovided with a eell-wall, possess evidently a 

 single nucleus, and present amoeboid movements, though in a much higher and more 

 active degree than the calciferous ones. It almost conveys the impression that the 

 process of absorption demands a much more intense labour on the part of the cell 

 than that of deposition. » 



Both kinds of cells, the calciferous as well as the absorbent, do not operate 

 independently hut each of them enters into communication with other cells of its 

 own kind, their protoplasm having run togcther and bccome mixed. In this manner 

 the calciferous and absorbent cells constitute syncytia or plasmodia, each on their 

 own account; there may be no perceptible differeuce in the structure of these two 

 syncytia, but a certaiu divergence seems 1<> exist with regard to their mode of ope- 

 ration and, of course, especially in their functions. 



The calciferous syncytia scein to be more eonstant and immovaMe, al least 

 unlil t lie larval skeleton has grown to the full, while the absorbent ones protrude 



slender pseudopodial Eilaments which give off branches and anatomose with each 



1 on the developmenl of Echinocyamus pusillus 10. v. M.) with nine plates. Roj Soc. Se. Upsala 1892. 



• Notes on the formation and absorption ut' the skoleton in the Echi lerms. öfveraigl af Kungl. 



Vetenskap akademiens Förhandlingar 1894. N:o 8. Comp. also the following paper ut' 1896: 



Remarks on the åctivitj of amoeboid cells in the Echiuoderms, with one plate. Festskrift tillegnad 



\\ . i.iiijri.uiv i psala L896. 



