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PROCEEDINGS OF TEE 



[Dec, 1856, 



In fact, Eurystoma and Pachysoma of the same author, appear 

 to be closely allied to Stenogaster and our embryo, and their 

 embryological history would be of the greatest interest. 



We have now traced the larva of Turritopsis through successive 

 changes, from its early condition of an untentaculated Hydra, to 

 that stage in which we find it a free swimming Medusa, So grad- 

 ual are these changes that it would be impossible to draw, with 

 precision, a line of demarcation between the Hydroid and Medusoid 

 stages, unless we say that the first appearance of the otolithic vesi- 

 cles should be so considered. But at that stage, the larva still has 

 a distinctly hydroid form, and still moves by its tentacula, like the 

 yet unfixed larva of Tubularia. And, indeed, the power of moving 

 itself in this manner, when resting upon any surface, does not ap- 

 pear to be wholly lost in the most advanced medusoid larva I have 

 seen. In short, -all these transformations lapse so gradually, one 

 into the other, that we may safely consider the development of 

 Turritopsis, so far, as genuine a metamorphosis, as that of the 

 caterpillar into the pupa among Butterflies. What changes follow 

 these, I have been heretofore foiled in every effort to discover, 

 With all my pains I have never succeeded in keeping this Proto- 

 medusan form alive for more than a fortnight, and in that time no 

 new change of importance can be observed. I have sometimes 

 believed that the triangular prolongations of the stomach were 

 lengthened in that time, assuming more the form of radiating 

 tubes, and that the tentacula at their apices, which are, the ocelli 

 only excepted, identical with those of the adult Turritopsis, had 

 approached more nearly to the outer edge of the disk; but this 

 observation has always been brought into doubt, by the circum- 

 stance that the larvae, at such times, have appeared more or less 

 sickly, and the stomach somewhat contracted, rendering it not by 

 •any means certain that the apparent elongation of those projec- 

 tions, was not merely a temporary change in apparent proportion, 

 of parts. Yet it would seem probable from the nature of the de- 

 velopment, so far as I have been able to trace it, that the Polyxe- 

 noid medusa is directly metamorphosed into a Turritopsis, exactly 

 in the same manner as Ephyra is into the adult Cyansea — and this 

 probability is certainly not lessened by the fact that the youngest 

 Turritopsis I have yet seen, and which was taken early in the sum- 

 mer (1856) had only eight tentacula, while a fully grown adult has 

 about one hundred. The eight tentacula of the medusan larva, 



