430 Mr. H. J. Carter on the Development 



now, as I am accumulating material for a separate paper on 

 this subject. 



In the development of the young Spongilla, I, of course, 

 had nothing to deal with but the acerate or primary form of 

 the spicule, as this is the only large form in this sponge ; but 

 in the young Tetliyce^ as will have been seen, there are arms 

 to many of the spicules, resulting in the development of se- 

 veral different forms, the chief of which, and that which is 

 peculiar to the young TetJiya, is the one-armed anchor-headed 

 spicule. 



To resume shortly what I have already stated in this re- 

 spect : — the development of the ovule commences with the 

 cell of cellules &c. in the sarcode ; then follows the breaking 

 down of all these cellules into a granular mass of plasma, of 

 an ovoid shape, appended by a pedicle to the outside of the 

 sarcode, in a dilated cavity of the excretory canal-system ; 

 then a few acerate spicules appear in the centre of this, toge- 

 ther with many minute spherical refractive granules, appa- 

 rently of a siliceous nature ; lastly, the granular plasma be- 

 comes areolar, the spicules greatly increase, and heads of 

 various forms develope upon their peripheral ends, among 

 which the one-armed anchor-headed one mentioned is not only 

 the most numerous, but, as before stated, extends somewhat 

 beyond the circumference of the young Tethya^ now become 

 globular. It is to this form, which appears in all stages of 

 development, that my attention has been chiefly directed ; and 

 from it I am able to add a little more to the development of 

 the spicule than I have already given. 



The four representations under fig. 16, PI. XXII. are in- 

 tended to furnish a series of forms illustrative of the develop- 

 ment of this one-armed anchor-headed spicule, which, of 

 course, will apply to all other developments of the same kind 

 of form : that of a is, of course, assumed, since, before the 

 end of the shaft begins to be inflated, there is no indication of 

 what it is to be, beyond a linear acerate form. I have drawn it 

 as open at the ends, though I am not certain if this state always 

 precedes the inflation, as it is frequently seen in the simple 

 acerate spicule. In h we have the inflation of the head, which 

 undoubtedly precedes the formation of the arm, together with 

 a terminal expansion of the central canal in a compressed 

 cellular form. Our figure c shows the first budding of the 

 arm and the extension of the central canal which leads to it 

 branching off beloiv the terminal compressed expansion; while 

 d not only shows the full formation of the arm, but that of 

 the one-armed anchor-headed spicule generally, attended by a 

 frequent occurrence, viz. the budding of another arm, e. All 



