46 W. WOODLAND. 



safranin (nigrosin is also good) in absolute alcohol for a fort- 

 night, washed thoroughly in Avarm absolute for a day or so, 

 stained for a few minutes in a saturated solution of lichtgriin 

 in absolute alcohol, again washed well in absolute, cleared in 

 xylol and finally mounted in balsam. In most cases the picro- 

 carmine specimens became too dark if also stained with 

 lichtgriin. 



The spicules of these three genera are all somewhat irre- 

 gular monaxons with a concentric structure when viewed in 

 section, and containing a larger or smaller amount of organic 

 matter, but they differ slightly both in size and shape accord- 

 ing to the genus. In Archidoris the spicules are much more 

 slender than in the other two genera, and do not attain such 

 a great length ; moreover, they do not possess a sudden 

 thickening situated midway in the length of the spicule like 

 those of the other two genera, and the nucleus of the sclero- 

 blast is much smaller both relatively to the size of the spicule 

 and absolutely, is spherical instead of oval and possesses a 

 distinct nucleolus. The spicules of both Goniodoris and 

 Lamellidoris are, as just mentioned, thickened at the middle 

 and in the latter genus this midway thickening (which is not 

 so prominent as in Goniodoris) often possesses one or two 

 large spikes. The spicules of Lamellidoris attain a much 

 greater size than those of Goniodoris, and are much smoother 

 in general outline. Corroded spicules exhibit straight-sided 

 regular outlines at the exposed edges, Avhence we may suppose 

 that nudibranch spicules, like most other calcareous spicules, 

 are essentially aggregates of calcite crystals. 



The nearest approach to the spherical concretion stage of 

 the spicule which I have observed is that represented in fig. 

 1. Without doubt the spicule originates, as in every other 

 case of simple spicules, in this form, but unfortunately my 

 specimens are not young enough to show this, although the 

 stages figured afford sufficient proof that this is the case. 

 The granule becomes a rod and the rod assumes the form of 

 the adult monaxon, growing over its entire surface (but, of 

 course, chiefly at the extremities) by the deposition of cal- 



