48 ARTHUR DENDT. 



carmine. In its centre is the nucleus, a spherical body 

 invested by a very thick and distinct membrane, and measur- 

 ing, together with its membrane, about 002 mm. in diameter. 

 The substance of the nucleus itself is very finely granular, and 

 stains but lightly. The nuclear membrane, however, stains 

 deeply. There is also a single spherical nucleolus which stains 

 very deeply, and is placed excentrically, touching the nuclear 

 membrane. 



I have found several ova exhibiting the structure here 

 described ; they appeared to be worth mentioning as show- 

 ing to what a degree of complexity the ovum even of a sponge 

 may attain, and also as affording some confirmation of my 

 views as to the mechanism of fertilisation of the ovum in 

 sponges generally. 



The above remarks deal only with certain points in the 

 structure of Halichondria panicea; for the benefit of the 

 student I may add that a fairly complete literature of the 

 species is to be found on p. 2 of the Report on the ' Challenger ' 

 Monaxonida. 



EXPLANATION OF PLATE V, 



Illustrating Mr. Arthur Dendy's paper " Studies on the 

 Comparative Anatomy of Sponges. IV. — On the 

 Flagellated Chambers and Ova of Halichondria 

 panicea." 



Fig. 1. — Small portion of a section vertical to the surface. Zeiss, F, oc. 3. 

 «, I, c. Different views of three flagellated chambers, i, I. Inhalant lacuna. 

 e. I. Exhalant lacuna, e. o. c. Exhalant opening of a chamber, sp. Spicules. 

 X. Protoplasmic processes connecting a collared cell with a stellate meso- 

 dermal cell (?). s. m. Sollas's membrane. 



Fig. 2. — An ovum suspended in a lacuna. Zeiss, F, oc. 2. env. Envelope 

 of the ovum. «. Nucleus. 7i. m. Nuclear membrane. no. Nucleolus. 

 ped. Peduncle. 



