180 THOMAS H. BRYCE. 



but their observations were confined strictly to the ovary 

 and the formation of its epithelium, and to certain points in 

 the characters of the nucleolus. Various observers have 

 treated specially of Echinodorm spermatogenesis 

 (Jensen, Pictet, and others), and many have studied the 

 morpholog-y of the spermatozoon, but of these Field (1895) 

 brings the latest account. Owing to the excessive minute- 

 ness of the chromosomes he seems to have confined himself 

 to counting them in the different phases. Haecker (1893) 

 published observations carried out on the living egg on the 

 germinal vesicle and nucleolus of Echinoderms, but does not 

 give any detail regarding maturation. 



Personal Observations. 



Methods. — My material was obtained from animals 

 freshly out of the water. ^ Small pieces of close on 

 seventy ovaries were fixed, embedded in paraflfin, and a 

 few dozen sections cut from each. These Avere all care- 

 fully examined, and when maturation was found to be 

 proceeding some hundreds of sections were cut and gone 

 over, and the details built up fi'om these. The fixative fluids 

 used were Flemming's strong solution, and Hermann's platinic 

 chloride and osmic acid mixture ; almost identical results 

 were obtained by both, and the small pieces of ovary — about 

 a cubic centimetre or a little more — were well fixed through- 

 out. At a later stage of the research, by way of control, 

 pieces of ovaiy were fixed in Boveri's picric and acetic acid 

 mixture, and sublimo-acetic acid, as well as Lindsay John- 

 stone's fluid. The picro-acetic nuiterial was unsatisfactory, 

 but the sublimate gave good results in some respects. The 

 chromatin was, however, much better differentiated by the 

 osmic acid mixtures, especially by Hermann's fluid; while in 



' Tlie material was obtained at tiie Marine Biological Station at Millport 

 in late March and early April. At the end of April and beginning of May 

 tiie ovaries are mature throughout. In January maturation has already 

 begun, and from that time onward the relalivc proportion of mature to 

 immature ova gradually increases. 



