Distribution of Saccammina s])hasricay etc, 11 



adherent organisms proceed from the host-shell at all, beinij in our 

 opinion a different organism altogether. 



In his opinion the sponge-spicules in these primordial cells are, 

 in a later stage of development, discarded and replaced by small and 

 subsequently in turn by larger stones, as the shell reaches what 

 he calls the Psammosphwra stage. This Psamniosphsera stage is en- 

 dowed by him with an irregular aperture, which in our opinion, of 

 itself removes it absolutely from the genus Psamrnosphsera. Tlie 

 sponge-spicules found in his Primativgehduse remain constant in 

 Crithionina mamilla throughout its lite-history, though more or 

 less masked by the larger material incorporated with them. 



In Saccammina sphserica, on the other hand, sponge-spicules 

 are very rarely incorporated in the substance of the shell-wall, ex- 

 cept in a few localities (in the Faroe Channel), where the species 

 adopts a very rough and characteristic type of structure, and uses 

 large tetractinellid spicules as a supporting framework for the shell. 

 (Plate I, figs. 15-19.) These Faroe channel types must be re- 

 garded as quite local and abnormal. They do not exhibit any 

 pronounced pylomtubus, the aperture being usually an irregular 

 and large opening, nearly flush with the shell-wall and lined with 

 pale cement. This variety does not appear to have been noted and 

 figured previously. 



It does not appear probable to us that Dr. Ehumbler's theory 

 as to the attachment of the primordial cells, and the extrusion of 

 the protoplasm between the attachment surfaces and the base to 

 which they are attached, is tenable, but it is hardly worth while 

 to discuss this, as it is absorbed by the larger question of the 

 identity of these attached organisms, which in Dr. Ehumbler's 

 opinion gradually detach themselves as they add larger stones to 

 their structure, and start on their own account as Psammosphderds 

 on their way to becoming Saccamminm. In his theory the detach- 

 ment may either be voluntary on the part of the young organism, 

 or fortuitous and accidental. 



Again, Dr. Khumbler undermines this part of his theory in 

 turn, by casting (6', p. 457) doubt on whether the young stage of 

 Saccammina is necessarily attached at all. But he proceeds im- 

 mediately to state that Brady " discovered small Saccammina (by 

 him called Psammosplisera) measuring 0*01 inch," and goes on to 

 say that they are merely primordial chambers formed by sand- 

 grains instead of sponge-needles. (In point of fact, Brady never 

 casts any doubt upon the Psammosph^ra attribution of these forms.) 

 He therefore concludes that tlie primordial cell, like the adult, may 

 ].e either free or attached, and tliereby appears to abandon liis 

 Crithionina-Psammosphdera-Saccammlna cycle upon which it ap- 

 pears to us his whole argument is based. 



We cannot agree with Dr. Rhumblei when he says (6', p. 458), 

 " I do not hesitate to trace back the .grrowth of the Saccammina shell 



