ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 563 



which eventually coalesce. Between the tail lobes the neurenteric canal 

 is probably represented. The hindmost part of the proctodeum persists 

 as the permanent anus. The produced hind extremity of the embryo, 

 which results from a coalescence of the tail lobes, constitutes the com- 

 mencing postanal section of the body, i.e. the rudiment of the tail or 

 tail-bud. The postanal gut is a new formation, secondarily growing out 

 of the hind wall of the anal gut. The dorsal series of organs in the tail, 

 which are formed behind the blastopore in connexion with the postanal 

 gut, are also of the nature of a new formation. Thus the tail in the 

 lamprey, which is not more than one-eighth of the total length, is a 

 secondary formation. It is to be regarded as the dorsal outgrowth of 

 the blastopore lip. Its development takes place only after the embryonic 

 organs are established in the rest of the body — that is, in the post- 

 embryonic larval stage. 



Chromosomes and Mendelian Inheritance.* — J. H. Schaffner dis- 

 cusses the chromosomes with a view to emphasizing the remarkable 

 parallelism between the activities of the complicated mechanism, of 

 nuclear division, and the predictable phenomena of Mendelian inherit- 

 ance, summarizing as follows : The chromosomes normally function as 

 individuals, and are segregated as such at each karyokinesis. The 

 •chromosomes do not conjugate or fuse, nor does their material mix in 

 the fertilization stage ; but each chromosome is carried through the 

 zygote stage as a definite individual. In the reduction division the 

 chromosomes show themselves to be definitely paired ; and the 2x 

 number of the zygotic individual represents two definite sets or comple- 

 ments of chromosomes, each one of the one set having its synaptic mate 

 in the other. A specific attraction develops between each pair of 

 synaptic mates during the prophases of reduction, resulting in an end-to- 

 end fusion in pairs and a subsequent folding side by side, so that a 

 bivalent chromosome represents synaptic univalents fused longitudinally, 

 at least in the ordinary elongated types of chromosome. The segrega- 

 tion of the univalents during reduction is according to the law of chance ; 

 therefore, each daughter-cell receives a full (x) complement of univalents, 

 some of the set being descendants of those brought into the zygote by 

 the parent-egg and some by the sperm. 



These processes are in harmony with the observed phenomena of 

 Mendelian inheritance. 



Reproduction, Heredity, and Death. f — V. Hensen discusses these 

 subjects with special reference to marine organisms. The conditions of 

 life in the open sea are on the whole simpler than elsewhere, and in- 

 vestigation is easier. Death is correlated with reproduction, and without 

 it — especially old-age death — reproduction would in early days have 

 become impossible in the crowded abundance of the open sea. The 

 death of the persona is to be distinguished from the death of the 

 personal form. In asexual reproduction and parthenogenesis the personal 

 form may be continued year after year without change in the offspring ; 

 but in cross-fertilization or allogamy a new form arises. In Protists 



* Ohio Nat., xv. (1915) pp. 509-18 (1 fig.). 



t Wiss. Meeresuntorsuch. Kiel, xvi. (1914) pp. 1-84 (20 figs.). 



