^/g'] Micro-Fauna, Botanic Gardens Lake, Melbourne. 81 



time of this examination, very plentiful, the growth of 

 colonies on small branches secured to stakes in shady positions 

 being watched for months. Very large aggregations were 

 found on willow roots and floating branches. The sexual 

 stages of this hydroid were not seen, although carefully looked 

 for. Some years ago a sedentary rotifer, Lacinularia elongata, 

 occurred very plentifully over a large area of the lake, but no 

 member of this group occurred similarly during the period of 

 this investigation. Megalotrocha alboflavicans came nearest to 

 it, being nearly always noted. Polyzoa of the world-wide 

 species, Plumatella repens, occurred in great quantity in 

 separated colonies. Another form, Fredericella sultana, was 

 found, but was not nearly so plentiful. The free-swimming 

 forms must be regarded as the best subjects to reveal indica- 

 tions of periodicity of occurrence. Volvox — claimed by botanist 

 and zoologist alike — although a slow swimmer, is certainly a 

 diffusible form, and was noted on every visit ; two species were 

 found — a monoecious form, closely resembling descriptions of 

 V. globator, and a dicecious species, which is probably V. aureus. 

 This latter greatly preponderated in number. Warm weather 

 evidently favoured the growth of this organism, for it was 

 found in the summer in enormous quantity. A relation was 

 established between Volvox and the parasitic rotifer Proales 

 parasita. Whenever Volvox was plentiful, then Proales was 

 found in numbers. Two of the workers were able to settle for 

 themselves the question as to how the rotifer finds its way 

 inside the hollow sphere of Volvox, for they were repeatedly 

 observed eating their way through the walls of their temporary 

 cage and swimming away in search of another victim. The 

 converse operation of entering another host was not witnessed, 

 but sufficient of the process was seen to leave no doubt that 

 entrance was similarly effected. Developing ova of Proales 

 were found in Volvox on several occasions. 



Regarding the three groups, Entomostraca, Rotifera, and 

 Protozoa, the two former were chiefly obtained by the system- 

 atic use of the tow-net, and the results in the case of the species 

 occurring with sufficient frequency are shown graphically on 

 the appended diagram, drawn up with the kind assistance of 

 Mr. A. D. Hardy. Besides the forms thus indicated there were 

 many others, the complete list of forms certainly identified 

 comprising twenty-two species of Entomostraca, ~ forty-eight 

 Rotifera, and fifty Protozoa. The most noticeable feature in 

 the list of Entomostraca is the absence of Daphnia carinata, 

 found in most of the ponds around Melbourne. It is a large 

 and variable species, and, when present in a pool, is generally 

 found in considerable numbers. On a visit to the lake some 

 two years prior to starting on this investigation, another — and, 



