228 SUMMARY OF CURRENT RESEARCHES RELATING TO 



fusiform, and are almost eutirely occupied by the nucleus which con- 

 tains one or more nucleoli ; in the black tissue the cells contain 

 black granules. The cone is made up mainly of lamellte, vary- 

 ing from a mere bud-like condition at the apex to that of the fully 

 developed trabecula at the base ; they consist each of a band of 

 connective tissue on which the above-mentioned epithelial elements 

 are based. An irregular circular opening at the anterior and upper 

 end of the gland transmits the secretion to the excretory sac. 



Genealogy of the Ammonites.* — L. Wiirtemberger finds that in 

 the first, that is, youngest whorls of the shell of Ammonites, the lobe- 

 lines which mark on the exterior the points of junction of the septa, 

 are always simpler than those of the adult chambers, often as simple as 

 in Goniatites ; hence they point to a derivation of the one form from the 

 other, and species of Ammonites with simpler lobes are to be considered 

 as more primitive in type. Again, branched ribs represent a state 

 derived from simple ribs, but the branching may go so far as to pro- 

 duce from each two ribs simple like the first. Spines and projections 

 first appear in the younger whorls ; therefore, the species which possess 

 them are further evolved than those which do not. Species which 

 have no ribs but have spines, carry their spines in the same positions 

 on the shell as they would if they had ribs, e. g. at the place corre- 

 sponding to the bifurcation of the rib, &c. ; therefore the rib-less is de- 

 rived from the ribbed condition. The occurrence of a marginal furrow 

 running on the outside of the shell in a position corresponding to the 

 siphon within, and serving to protect this organ, is a more highly 

 evolved condition than that with a plain margin, and the addition of 

 spines to this region with the same protective object must be consi- 

 dered as marking a further step in advance. Now, when these spines, 

 in obedience to the law of occurrence of the ancestral condition, appear 

 in the younger segments of the disk-like shell, they occupy so incon- 

 venient a position with regard to its growth, that a lateral deviation 

 from the spiral form is introduced, producing such forms as Crioceras, 

 Hamites, Turrilites, the latter of which, in accordance with the theory, 

 appears quite late in the series, viz. in the chalk. The genealogy of 

 the Jurassic Ammonites thus commences with the Liassic Planulate 

 forms (A. communis, anguinus, annularis), from which are derived the 

 Armati (Aspidoceras), on the one hand, and on the other the Polyplocus 

 forms of the White Jura. The series is to be considered as mono- 

 phyletic, i. e. but one chain of forms exists. 



Gustatory Organs of the Heteropoda.f — From a preliminary com- 

 munication from Professor Todaro, we learn that the gustatory bulbs 

 are set in two or three rows on each side of the buccal cavity, and 

 that in Pterotrachea they extend a little beyond the enlarged extremity 

 of the proboscis. The bulbs are invested by the epithelial layer of 

 the buccal mucous membrane, and by a cuticular layer, which is 

 pierced by a pore at the tip. In structure they resemble the same 

 organs in mammals ; the sensory cells form a cone, and have a large 



* Naturforscher, xiii. (1880) pp. 370-1. 



t Arch. Zool. Exper. et Gen., viii. (1880) (Notca et Rev.) p. 1. 



