42 Journal of the Mitchell Society. [Match 



infrequently in a related species. For instance, in Caulopha- 

 cus schulzei the pinuli occasionally have the shape characteris- 

 tic of C. latus and C. elegans. A striking case is afforded by 

 Farrea occa claviformis, in which a few gastral clavulae were 

 found closely similar to the peculiar clavulae of Farrea 

 convolvulus. 



8. Constancy of character in spicules. 



It often happens that while in a single individual the size 

 of a particular spicule may vary within wide limits, the char- 

 acter remains fairly constant — e. g. pinuli of Hyalonema bian- 



choratum. The character of a spicule even in minute 



details may apparently become fixed for the species. Thus in 

 a specimen of Hyalonema ovulifernm the rays of the micro- 

 oxyhexacts have the same sudden terminal curving exhibited 

 by the corresponding spicules of Schulze's type specimen, 

 although the two sponges were taken 49° of latitude apart. 



A form of spicule which in some sponges varies greatly 



in size, in other species varies but little. Thus in Gellius 

 pe?'foratus the sigmata vary only slightly, whereas in lylo- 

 desma alba they vary greatly. 



I do not undertake a comparative consideration of the geo- 

 graphical distribution of the forms making up the collection. 

 Such a consideration would demand a knowledge of the actual 

 systematic value to be attached to many species recorded in 

 the literature of sponges. And such a knowledge is not to be 

 had at present. In modern sponge literature, e. g. in the two 

 great monographs of Schulze and Sollas (Schulze, 1887; Sol- 

 las 1888), the species conceived are, as it seems to me, what 

 H. M. Bernard contends for in his interesting recent discus- 

 sions (Proc. Cambridge Phil. Soc. Vol. XI. Pt. IV.; Verhdlg. 

 V. Intern Zool. -Congress) of the species-question as affecting 

 the method of recording certain data, viz. homogeneous mor- 

 phological groups. The sponge species are often very homo- 

 geneous, because represented by single specimens. That such 

 groups answer always to natural species, as we understand 

 the word when we speak of the human race, Passer domestic 



