422 NOTES AND MEMORANDA. 



that in the Macrura these bodies are larger than in the Brachjura, and 

 within the limits of any group the spermatozoa seem to be proportional 

 in size to the general size of the body ; greatly as they vary in size, 

 they vary in form still more, and the dictum of Wagner that the 

 Vertebrate siiermatozoa may even vary in various S2)ecies, may be com- 

 pletely applied to the Decapoda, and the influence of this variation 

 on the j)reservation of species is insisted up(m, inasmuch as it is 

 obvious that the more the spermatozoa vary in character, the less will 

 they be able to set up the molecular changes by which fertilization 

 commences, in the females of other species than their own ; and 

 further, those species are most likely to be preserved that have highly 

 differentiated spermatozoa. 



The sum of the rays appears to be homologous with the flagellum 

 of the Vertebrate spermatozoon, and it is pointed out that immobile 

 spermatozoa are never found in any animal in which chitinous struc- 

 tures are not developed. 



IV. Vasa doferentia. The author distinguishes in these three 

 chief regions : (1) An efferent portion, which is delicate ; (2) a broader 

 glandular portion, and (3) a ductus ejaculatorius, which is ordinarily 

 provided with a very powerful musculature. This duct may give rise 

 to lateral dilatations of various sizes, which seem to provide a men- 

 struum for the sperm. Their presence has been frequently denied. 



V. Spermatophores. All the Decapoda examined by the author 

 form spermatophores, the envelope for which is ordinarily formed in the 

 vas deferens; in Astacus, this envelope is of a dead- white colour, 

 which hardens in the water, while the envelope of Homarus swells up 

 under the same conditions. In form these spermatophores vary 

 greatly : they are bluntly conical in Scyllarus, stalked in Eupagurus, 

 pouch-shaped in Porcellana ; in other BracJiyura there is no special 

 form for the different members of the group, and in Dromia there can 

 hardly be said to be a spermatophore at all. 



B. External Generative Characters.— As is well known, there is an 

 easily recognized difference between the male and female; of the 

 accessory generative characters by which this is effected, some are due 

 to the development of other organs, such as the ovary, and may be 

 shown to owe their origin to natural selection ; others are due to the 

 development of parts which have for their purpose the safety of the 

 sperm or of the young, and these have a similar origin ; others, again, 

 are due to sexual selection, such as the offensive organs formed by the 

 appendages of the males, or their coloration ; while the last set of all 

 are dependent on the different modes of life of the two sexes. 



G. A few brief observations are made on the vascular supply of 

 the generative organs, in which the antennary and sternal arteries take 

 a large share : a species of Distomum was observed in the vas deferens 

 of Portunus depurator. 



Central Nervous System of the Crayfish. — In a brief communi- 

 cation,* consisting of histological and of morphological observations, 

 Krieger states that the perineurium consists of a firm membrane, in 



* ' Zool. Anzeiger,' i. (1878) 340. 



