48 SUMMARY OP CURRENT RESEARCHES RELATING TO 



ampullae kept np a circulation in the isolated lobe for about two weeks, 

 after which buds re-appeared in it. An examination of half the colony 

 showed that there were small isolated buds, probably produced by the 

 zooids which had degenerated, scattered all through the colony. The 

 colony gradually recovered its former condition, except that it always 

 retained its yellow colour, which is characteristic of Botrylloides luteum 

 von Drasche. Therefore this species is a seasonal variation of B, f/ascoi. 

 During rejuvenescence the colony differed from the normal colony in 

 various ways, which are particularly described. The cause of these 

 deviations from the normal seems to be the inadequacy of the food 

 supply. This case of aestivation is in general similar to the hibernation 

 described in various Ascidians. 



INVERTEBRATA. 



Mollusca. 



Scientific Value of Conchology.* — 0. Boettger supports the claims 

 of the study of molluscan shells. He speaks of the problem of their 

 coloration, suggesting that the pigmentation (often hidden more or less 

 completely from sight) is an organised way of dealing with guanin-like 

 waste-products. He refers to the modifications of shell-form in different 

 localities and conditions, to the varied protective values of the shell, to 

 phenomena of variation and convergence, and so on. The study of 

 shells is rich in data of biological interest. 



■y. Gastropoda."! 



Spermatozoon of Helix pomatia.t — A. Bolles Lee has made a 

 detailed study of this spermatozoon. The head consists of two portions, 

 an exosome and an endosome, the former partially enveloping the latter, 

 and containing all the nuclein. The tail or bodv consists of an axis 

 cylinder and a tubular membrane, the exolemma surrounding it. Platner's 

 spiral fibre is an illusion. 



The axis cylinder consists of two fibres wound together and im- 

 bedded in a granular substance, the whole being enveloped in a structure- 

 less membrane, the endolemmn. The exolemma is not cytoplasmic, it is 

 a delicate membrane provided internally with a spiral thickening. 



The neck is an articulation, adapted to allow the ready separation of 

 the head. Neither in the neck nor elsewhere is there any centrosome. and 

 there is no distinct Mittehtiirlc or " segment moyen," such as is seen in 

 Urodela. 



Notes on the Pleurotomidas.J — Thomas L. Casey discusses this large 

 family, basing his study on a review of over 600 species, living and 

 fossil. He discusses the vexed question of genera, and compromises 

 by dividing the family into eight more or less definitely limited and 

 definable " tribal groups," and regarding most of the subdivisions under- 

 these tribal headings as true genera until their values can be determined 

 more accurately. 



* Ber. Senckenberg. Nat. Ges., 1903, pp. 177-86. 



t La Cellule, xxi. (1904) pp. 79-117 (1 pi.). 



X Trans. Acad. Sci. St. Louis, xiv. (1904) pp. 12:>-70. 



