178 SUMMARY OF CURRENT RESEARCHES RELATING TO 



posited in the University Museum, Adelaide. The collection comprises 

 seventeen or eighteen species (in seven genera), and at least half of these 

 species are new, though most show a close affinity to living forms. 



5. Lamellibranchiata. 



Spawning Period of Mussels.* — A. Scott records a series of obser- 

 vations on this subject made on tank specimens of Mytilus edulis, but 

 constantly checked by comparison with forms living under natural con- 

 ditions. The mussels began to discharge eggs on May 6th, and this 

 continued without any corresponding discharge of sperms until June 

 13th, when the sperms first made their appearance. Two days after 

 the first appearance of sperms another discharge occurred, and though 

 sperms were not again observed, all the subsequent eggs proved fertile. 

 Prior to June 13th none of the eggs developed, and all were apparently 

 unfertilised. Fertilisation is apparently effected internally. After 

 being shed the ova fall to the ground near the parent, and here remain 

 for eight to twelve hours, during which they undergo the earlier stages 

 of development. They then rise to the surface and enter upon the free- 

 swimming stage, which lasts about four days. 



Arthropods. 

 a. Insecta. 



Chitin-Formation, Muscle-Insertion, and Cell-Connections in In- 

 sects.f — Nils Holmgren has studied these subjects in Sarcophaga car- 

 naria, Musca vomitoria, and Chironomus larvae. He confirms Tullberg'& 

 conclusion (1881) that chitin usually arises from a direct transformation 

 of the distal parts of epithelial cells. The same occurs in muscle-cells. 

 Only in one case could it be said that the chitin was formed as a secre- 

 tion of the epithelium, as Biitschli, referring to tho egg-shell of the 

 crayfish, maintained against Tullberg. 



In the vagina of Sarcophaga the matrix-cells form parallel lamella* 

 of chitin ; in the efferent ducts of the sperm-capsules the filar substance 

 of the cells is gradually chitinised distally, but into pillars, not lamellae ; 

 in the median oviduct of Musca the couical matrix-cells are prolonged 

 into points (chitinised only at their tips), and between these threads 

 almost structureless chitin is formed — mainly as a secreted product. 



Holmgren shows that before a muscle-cell reaches the epithelium it 

 loses its striation. Its fibrils enter the epithelial cell, traverse its whole 

 length, and end with a chitinised portion in the epithelial chitin. Besides 

 the connections between epithelial cells and those between muscle-cells 

 there are very distinct direct connections between epithelial cells and 

 muscle-cells. 



Spermatogenesis in Insects.ij: — Walter S. Sutton has studied the 

 spermatogonial divisions in the grasshopper Brachystola magna, with 

 special reference to the chromatin. The adult testis displays sperma- 

 tozoa near the collecting duct, spermatids a little further lip, and finally, 

 in some cases, primary and secondary spermatogonia. Preparatory to 



* Proc. and Trans. Liverpool Biol. Soc, xv. (1901) pp. 161-4. 



t Anat. Anzeig., xx. (1902) pp. 480-8 (6 figs.). 



% Kansas University Quarterly, ix. (1900) pp. 135-60 (4 pis.). 



