32 



PORIFERA. II. 



form as the normal spicules of the species; the not-swollen end is rounded or quite slightly dilated, 

 in other words it has quite the same form as in the normal spicules, and consequently it is the point 

 of the spicule that is transformed. Also its position agrees with this view, it having, like the other 

 projecting spicules, the head-end turned inward. This spicule, which occurs here so scattered and in 



small numbers, must be regarded as an abnormal form, and in the 

 bundles transitional forms are also found with slightly swollen or 

 only rounded outer end. That the spicule should be of extraneous 

 origin is quite out of the question, as well on account of its form, 

 as its always occurring in the same way. - It would seem that 

 projecting dermal spicules upon the whole are somewhat liable to 

 be influenced with regard to the form, especially of the outer end, 

 of which among others Mycale placoidcs furnishes an instance bv 

 its dermal spicules that vary so characteristically in different indi- 

 viduals. 



The occurrence of this spicule, however, is not without 

 interest, as it is of a quite similar form and occurrence as the 

 dermal spicules in Rhaphidotheca MarsJiall-Hallii Saville-Kent (Ann. 

 Mag. Nat. Hist. 4. Ser. VI, 219, PI. XV, figs. 1 — 7) from the coast of 

 Spain, and Rhaphidotheca afjinis Carter (Journ. of the Roy. Micr. 

 Soc. II, 497, PI. XVII, figs. 1 and 3) from a locality between Scot- 

 land and the Faroe Islands, which latter species is probably identical 

 with the former '). This species has the common Mycale-spicxilation 

 quite as in lingua, but in all, or almost all, the spicules of the pro- 

 jecting bundles the outer end is swollen in a pear-shaped manner. 

 (Saville-Kent says expressly that a few pointed spicules are 

 found in the bundles.) In this species the feature has thus no doubt 

 become normal for all or almost all projecting spicules. The opinions 

 advanced by Carter (Ann. Mag. Nat. Hist. 5, I, 170, Journ. of the 

 Roy. Micr. Soc. 1. c, and Ann. Mag. Nat. Hist. 5, IX, 299) that these 

 spicules should be foreign and embodied by the sponge, and that 

 their form should have been altered by the sponge after the em- 

 bodiment, with reference to which latter fact he, in the place last 



quoted, even says: « has been shown to be adventitious or 



appropriated, having first belonged to another sponge», are devoid of all foundation, and it is a 

 peculiar thing that Carter has not been able to see, from their form and way of occurrence, that 

 they belonged to the sponge. The whole question debated in the places quoted, whether needles may 

 occur turning the pointed end inward in the sponge and projecting with the head-end, is likewise of 

 no consequence, as it is a fact that the mentioned spicules turn their head-end inward in the sponge. 



Fig. 1. X165. 



■) Vosmaer (Notes from the Leyden Museum, II, 141, 8) refers, with a query, Rhaphidotheca Marshall-Hallii, as a sy- 

 nonym to Espcrella nodosa O. S. In the description of Schmidt, however, there is no base at all for this referring. 



