TRANSACTIONS OF SECTION D. 735 



wide g-eographical distribution ; thej'have been brought home by the 'Challenger,' 

 the ' Vettor Pisani,' the * National,' and the ' Albatrosp,' but it is to be noticed 

 that they have been caught only in those really oceanic exphn-ations, so, if they are, 

 not deep-sea Medusje, they are certainly not forms of the shiillow water. 



Amongst the Polypomedusje we iind a -very close relatioi'sbip between Atlantic 

 and Pacific species. The different species of one genus are in general much more 

 difficult to distinguish than amongst the Trachomedusse. This perhaps may be 

 explained by the eflective power of passive dispersal. 



3. For the first time a great number of sketches of living material of the 

 Periphyllidfe, &c., had been obtained on board. All these show the dark purple 

 colour, generally attributed to deep sea animals. The explanation for other forms 

 is, that in the green phosphorescent light of the abysses, purple is the comple- 

 mentary colour, which makes the animal invisible, and acts as a protective colour. 

 It would be dangerous to conclude from this that Periphylla, &c., are deep-sea 

 forms. They have been brought up in an open trawl from a great depth, but the 

 closed part of the net contained no Medusae. If a haul from a great depth con- 

 tains forms which did not occur in surface hauls, these forms do not necessarily 

 come from the abyss, for they might have been caught on the way to the sur- 

 face. Our knowledge of the pelagic life of the surface is still so incomj^lete 

 that every expedition brings us new species, as has been shown in the Copepoda, 

 MedusEB, and other groups of the 'Albatross ' Expedition. 



4. On the Sjoermatogenesis in Birds. By J. E. S. Mooee. 



The observations were made to ascertain whether the course of the spermatogenesis 

 in birds was essentially similar to that of other vertebrates recently examined. 

 It was found that in two points of chief importance, namely, the manner of nu- 

 merical reduction of the chromosomes and the alternation of the homo- and hetero- 

 type divisions, the spermatogenesis of birds is closely similar to that of the remaining 

 vertebrate forms. 



During the first heterotype division, which corresponds to the division of the 

 growing cells in Mammals and of the great spermatocytes in Elasmobranchs and 

 Amphibia, the spermatic elements of pigeons show a marked tendency towards 

 the formation of multinucleate masses. One of the most interesting features apper- 

 taining to these bodies is that the spindle-figure during the division of their nuclei 

 appears to originate entirely within the nucleus, since the nuclear wall can be 

 distinctly seen after the spindle-figure has been fully formed. The stages in the 

 division may be diagrammatically represented thus : — 



Multinucleate Spermatocyte of Pigeon, 

 (a) Nucleus in synaptic phase. (6 and c) SpintUe-figurcs. (im) Nuclear waU. 



The advent of the great heterotype mitosis is always preceded during the 

 spermatogenesis by the peculiar convoluted and lop-sided figure {a> which is 



