EEPORT ON THE MONAXONIDA. xlix 



Lastly the sponge may be lipostomous, i.e., without any visible oscular openings at all ; 

 such appears to be the case, commonly at any rate, in the deep-sea genera, Cladorhiza 

 and Chondrocladia (PI. XX.). 



General Kemarks on the Canal System. 



We may briefly sum up our more important conclusions with regard to the canal 

 system of the Monaxonida as follows : — 



(1) The arrangement of the pores varies almost indefinitely, being to a large extent 

 dependent either directly or indirectly (through the dermal skeleton), upon the external 

 conditions under which the species lives. They may be scattered all over the sponge or 

 localised in more or less definite areas. 



(2) The canal system in the Halichondrina, usually if not always, belongs to 

 Vosmaer's third type,^ that is to say, it is more or less lacunar, and the flagellated 

 chambers open by wide mouths into wide exhalent lacunae. In the Clavulina the canal 

 system may belong either to the third or fourth ^ types ; in the latter case the flagellated 

 chambers are provided with special " cameral canaliculi." 



Thus our general conclusions with regard to the type of the canal system are quite in 

 accordance with those of Vosmaer'' and Polejaefi".* It is true that two naturalists have 

 attempted to establish the existence of a racemose type of canal system in Halichondrine 

 sponges. Keller's attempt^ in the case of Reniera semituhulosa has been already 

 severely criticised by Polejaefi'," who comes to the conclusion that " the observation of 

 this naturalist on the structure of Reniera semituhulosa, executed under the influence of 

 Professor Haeckel's statements on the non-existing racemose type of the canal system " 

 is " unreliable"; a conclusion which we cannot but endorse. The second attempt does not 

 appear to have attracted much attention, and certainly does not deserve to do so ; for, 

 whatever may be the sponge which Saville Kent' mentions under the name Esperia sp., 

 we are confident that it never had a canal system of the quite impossible kind 

 figured, in which the diameter of the flagellated chambers is about twice that of the 

 pores, and there are (to judge from the figure) no exhalent canals whatever. 



1 Vide Bronu's Klass. u. Orduuiig. d. Thierreichs, Porifera, p. 130. 



'^ Loc. cit. 



^ Bronn's Klass. ii. Ordnung. d. Thierreichs, Porifera, p. 335. 



* Zool. Chall. Exp., part xxxi., Eeport on the Keratosa, p. 80. 



'' Zeitschr. f. wiss. ZooL, Bd. xxx. p. 579, pi. xxxvii. fig. 1. 



^ Zool. Chall. Exp., part x.xxi.. Report ou the Keratosa, p. 79. 



' Manual of the Infusoria, vol. i. p. 169, pi. vii. fig. 2. 



(zool. chall. Exr. — part lix. — 1887.) Nnu g 



