58 W. WOODLAND. 



Now the only direct way in wliich to prove or disprove 

 this supposition that spicular forms are inherited is to rear 

 spicule-bearing organisms in water deprived of the material 

 necessary for the formation of the skeleton. If we do this 

 we shall then, if the sup])Osition be correct/ find that the 

 scleroblasts in an echinoderm, e. g. will form moulds of the 

 plate or more complicated spicules, differing only from those 

 formed under normal conditions in that they do not contain 

 spicules. Is there any evidence to prove or disprove this ? 

 The only experiments conducted on the lines just described 

 that I know of are those which were performed by Maas 

 (13. 14) in 1904 on calcareous sponges, and by Herbst (9) in 

 1892 on echinoplutei. Unfortunately, these experiments 

 Avere but of little value so far as they relate to the present 

 problem since the spicules of Calcarea and plutei are not 

 wholly enclosed by cell-substance (the hypothetical moulds) as 

 most other spicules are, but simply increase in length and thick- 

 ness in the same way as a hair or horny fibre does (Study VI), 

 and the dispositions of thecells^ associated with the formation 

 of these spicules (which dispositions were produced in these 

 experiments) are not such as to be solely related to the forms 

 of the spicule but are brought about by other causes (Studies 

 I and III). Up to the present then we possess no experi- 

 mental evidence that the form of the spicule is determined 

 by a scleroblastic mould/ and the direct proof or disproof of 



formative forces are in no essential way different from those which are 

 everywhere exhibited in the shaping of the living organism and its parts." 

 (Schulze [23] ; similarly Maas [15]). 



' And if the altered chemical conditions of existence have no pathological 

 effect on the development of tlie organism — which substantially appears to be 

 the case according to the experiments of Maas and Ilerbst, referred to below. 



- Ilerbst says nothing about a triradiate mould being formed in one of the 

 constituent cells of each lateral cluster; but then, of course, he did not look 

 for one. 



^ Even in calcareous sponges, in which a kind of "mould" is stated to 

 normally occur (Minchiu [17J, Woodland [Study I]), this in all probability is 

 but a preliminary deposit of horny matter, which later forms the spicule- 

 sheath (Minchin). The instances of cell "moulds" described by Chun 



