B. Special. 2. Demospougiae. U 



the growing sponge round the growing Pagurus; where the umbo of the 

 shell is "long it serves as a columella, and the cavity may continue with great 

 accuracy the spiral of the shell; in other cases its spiral may be highly 

 irregular. The relations of rotation to growth may be measured by the fraction 



angle of rotation , ., 



- -, - = mean velocity or cyclic motion [misprinted m text] ; this 



attains its highest value when the crustacean is small and the growth of the 

 sponge mainly parallel to the axis of the vestibule. Most specimens showed a 

 vestibule of 1 to 2y 2 complete turns; one of the smallest specimens showed 4 

 complete turns, the largest number yet observed. - - History. One inhabited shell 

 shows over part of it a thin crust of S. Renier held that the larva fixes itself on 

 a shell already annexed, but if motion is no bar to fixation, why has C. failed to 

 find Snberites among the Polyzoa and Coelenterates on the shells of living Mol- 

 luscs? In many cases Serpula tubes inside the shell prove that it was dead before 

 the entrance of Pagurus, yet if this was delayed long after fixation of the sponge, 

 the mouth of the shell would be closed. Further facts are required. The house- 

 hunting appears, since the apertures of the shells vary in size from 2 to 20 mm., 

 to occur in the life of the Pagurus at very different times. The problem is not 

 helped by observations on Dromia, which possesses itself of an already grown 

 Suberites] it is held in the desired position, and never adheres. C. would expect 

 S. domuncula to be found also attached to fixed and inanimate objects, and be- 

 lieves he has identified such a specimen [see supra p 8 Levinsen], Form. Os- 

 cula appear confined to the superior and posterior surfaces, cavities containing 

 Amphipoda to the former ; the author points out that with the spiral growth of 

 Pagurus the upper surface of the sponge must become lower, and again the con- 

 trary. Globular and ovoid sponges are found of all sizes, the smallest specimens 

 are generally pear-shaped, the largest irregular and lobate. - The pigment- 

 cells are compared to Zooxanthellae, having distinct cell-walls. 



Spongillidae. - See also Stedman, Hartog and Topsent( 4 ). 



Famintzin [v. Bericht f. 1891 Protozoa p 7] concludes that in Infusoria and 

 Spongilla the Zoochlorellae are to be considered as true algae of the family of 

 Protococcaceae, which have wandered into the animal from the exterior . A liv- 

 ing amoeboid cell in Spongilla was seen containing in a vacuole a still living Cili- 

 ate, while another cell had half engulphed a Scenedesmus acutus [cf. Metschnikoff, 

 Zeit. Wiss. Z. 32. Bd.]. From such ingested organisms are derived the starch-bo- 

 dies described by Lankester and Keller. [See also infra p 13 Weltner( 5 ) and in- 

 fra, Allg. Biologic p 1 Bouvier]. 



Topsent ( 2 ) finds Ephydatia jluviatiUs from the first lake of the Jordan not differ 

 sensibly from French specimens. Early in May, with surface temperature 23 C.. 

 the specimen (from the border of the lake) is full of innumerable healthy gem- 

 mules. Hence the absence of gemmules in Potamolepis Barroisi [cf. Bericht f. 

 1892 Porif. p 6] under similar conditions is probably an indication that this 

 sponge does not produce them [but see infra p 12 Weltner( 5 ), E.Jluv.}. 



Weltner ( 2 j finds that the name Spongilla erinaceus was used by Ehrenberg in 

 1841 for Euspongitta lacustris Auctorum ; therefore S. erinaceus, Lieberkiihn 1856, 

 must now be known as Trochospongilla horrida, Weltner 1893. 



Weltner ( 5 ), summarizing first the views of other authors, describes the gem- 

 mule of Spongillidae. The soft contents are surrounded by a capsule, usually 

 many-layered ; the innermost cuticle is always present ; except in Parmula brownii 

 it is pierced by one or more pores, shut in the winter. Next this cuticle is the 

 air-chamber layer, generally obviously cellular, though in a few species the 

 cells are very small ; they contain air-vacuoles, the section resembling a vegetable 



