ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 751 



repairing broken arms ; tliis rupture is often followed by a process of 

 reproduction, numerous cases of which are already known. These 

 facts may be as easily explained by the theory of Hackel as by that 

 of Perrier, but there are others which can only be explained by the 

 latter. 



The hard parts around the mouth are, it is well known, very 

 difficult to homologize with the ambulacral and adambulacral ossicles 

 of the arms ; but it is necessary to do this, if we regard the disk as 

 nothing more than a fused part of each of the arms. On the other 

 hand if either disk is an independent piece no homology is possible. 



We sometimes find specimens in which a broken arm becomes 

 bifurcated at its free end ; if the buccal angles were merely formed by 

 the union of the pieces of two neighbouring arms (as ought to be the 

 case on Hackel's theory) it is difficult to see why the angle of bifurca- 

 tion should not be formed in just the same way. On the other hand, 

 if the peristomial skeleton belongs to a central individual it is evident 

 that an arm could not produce along its own course pieces similar to 

 those of the central piece — the odontojjhors or the teeth. Between the 

 oral angle and the angle of bifurcation at the free end differences may be 

 observed in the spines, which in the latter are exactly like the adam- 

 bulacral and different from the longer ones found at the angle of the 

 mouth ; the brachial angle is formed by adambulacral pieces, which 

 are veiy different from the large truncated teeth of the peristome ; 

 and, lastly, the odontophor which is so characteristic a part of the 

 disk, is altogether wanting at the angle of the brachial bifurcation. 

 The author adduces photographs in support of these statements. 



Pourtalesia.* — Professor S. Loven, the veteran author of the 

 ' Etudes sur les Echinoidees,' has made another important contribu- 

 tion to the morphology of the Echinoidea, based on a study of the 

 characters of the remarkable deep-sea genus Pourtalesia. 



The first chapter deals with the general form of the skeleton, 

 which, as in all Echinids, is a hollow sac inclosing the visceral 

 organs, and constituted by three distinct systems — ambulacral, peri- 

 somatic or interradial, and calycinal or apical. The mode of numbering 

 suggested in the ' Etudes ' is here again made use of. Whenever this 

 skeleton has been accurately stuilied it has been found that its con- 

 stituent elements are, in reality and fundamentally, arranged bilaterally 

 and symmetrically on either side of the mesial plane, indicated by its 

 anterr^-posterior axis. The archaeonomous or old-fashioned type of 

 the Clypeastridae as well as the neonomous or new-fashioned Spatan- 

 gidce give distinct indications of the bilateral form of the adult. 

 Though more difficult to detect, this bilaterality obtains also in the 

 ancient Cidaridee, and we have here " another instance of the validity 

 of one of the laws more than once ascertained to underlie evolution, 

 namely, that structures which are to be gradually but forcibly worked 

 out during the course of geological ages into specialized and highly 

 characteristic features, arc virtually present within the fabric of the 



♦ K. Svcnska Vet. Aka<l. HiukII., xix. '1883) Do pii. ('21 \th.) (writtcu in 

 EiigliBli). 



