PORIFERA. I. 



and sliut, I have thouglit it serviceable, as a rule, to give the measured limits of the sizes of the pores 

 in the different species. 



By the examination of the spicnlation and the spicules I have especially endeavoured to give 

 exact measures, as also to give figures of the different forms. As the spicules prove to be upon the 

 whole constant with regard to size and form, they form the best specific characters. At the same time 

 I have tried, as far as possible, always to find the younger phases of the individual forms of spicules, 

 which I have drawn together with the pictures of the fully developed spicules. B}- this examination 

 it has proved to be a general rule that almost all spicules are begun in about their full length, and 

 then the growth takes place exclusivel>- by apposition, and sometimes by apposition after fixed lines. 

 A growth in conformit}- with the organic growth does not take place, neither any growth by con- 

 temporaneous resorption and apposition. According to this the yoimger spicules must always be 

 inscribable in the full\- developed ones, and from this follows again with regard to the microsclera 

 that the smaller forms are not, as is commonh' stated, forms of development of the larger ones, but 

 independent, full\- developed spicules')- If, for instance, we have a sponge with sigmata, and these, 

 as is generally the case, are varying in size, then the smaller sigmata are not young forms of the 

 larger ones; by apposition the smaller ones would only become thicker, but very little longer. That 

 this view is correct is corroborated by the finding of quite thin young forms having almost the same 

 length as the grown ones. In the single cases account of this fact has been more particularly rendered 

 by the description of the species. In this respect the sponge-spicules, as will be seen, form a parallel 

 to the silicious shells of the diatoms, which, once formed, do not show an\- growth, properly so called, 

 but only grow b\- apposition partl\- after fixed lines. Of microsclera I have in this part only treated 

 of the forms found in Heterorrhaphidse. With regard to the chelte and anchorse quite the same thing 

 has been fully shown by Levinsen (Studier over Svampe-Spicula. Vidensk. Medd. fra den naturh. 

 Foren. i Kobenhavn for 1893. 1894), and in the next part of the present work I expect to corroborate 

 the statements of this author for a great number of forms. 



As to systematism I have, for the forms treated of here, chiefly followed Ridley and Dendy, 

 partly also Topsent. I have kept the family Heterorrhaphidce of Ridley and Dendy, as it seems 

 to me to be naturally enough bounded, and I do not, as does Topsent, think that we are more 

 justified in using the megasclera than the microsclera as distinguishing characters. The famih- Poeci- 

 loscleridce of Topsent, which is chiefly characterized by monactinal megasclera, includes nevertheless 

 the genus Desmacidon s. 1. with diactinal megasclera, and this genus is chiefl\' distinguished from 

 Gellwdes by its having chelate microsclera; if no regard is paid to the microsclera as a distinguishing 

 character, Gelliodes might as well be classed with the Poeciloscleridce. On the other hand I think 

 with Topsent that Tcdaiiiiiia; b\- their spicnlation are related to t\\e DendortcmcB, and therefore they 

 have not been included here; at present more genera without chelate microsclera or quite without 

 microsclera are known, which nevertheless no doubt must be classed with the Desinacidonidcv. 



As I have explained more particularh- in the mentioning of the genus Phl(Eodictyoii [Rliiso- 



■) I must, however, here notice that O. Schmidt (Spongien d. adriat. Meeres 1862, p. 9 — 10), although with regard 

 to these spicules supposing a growth like the organic growth, says of (die charakteristischen hakenfomiigen Korper der 

 Gattung Esperia : In eiuigen .\rten kommen ... kleinere und grossere Formen vor, allein dies sind in einer und derselben 

 Species zwei Arten solcher Korperchen, nicht junge und alte >. Thus he has correctly interpreted this phenomenon. 



