HYDROZOA. 
GceL 10 
a special department of an arctic circumpolar fauna. R. Sciimidtlein, 
“Beobachtungen iiber Trachtigkeit- und Eiablage Perioden verschiedener 
Seetbiere,” MT. zool. Stat. Neap. i. pp. 124-126 {Anthozoa, Acalephce, 
Siphonophora, Ctenophora, &c.) 
Morphology, Anatomy, and Physiology, &c. 
The circular arrangement of the tentacula in certain Hydrozoa is, accord- 
ing to Mereschkowsky (17 a), a case of “ metamerism,” of incomplete 
transversal division [!]. The Hydrozoa of this type are designed as 
the “ articulate” type ; they are almost always provided with capitate 
tentacula, the form best adapted to the function of defence, the only 
one remaining to them, when their position has become too distant from 
the mouth. Capitate tentacula are very rarely found in “ non- 
articulate ” gymnoblastic Hydroids, whose scattered tentacles are always 
filiform, long, and very supple, never in Thecaphora. A hydranth is, 
according to the author, properly speaking, not an individual, but a 
polymorphic colony of Protohydrm" and Archydrce” each tentacle 
being like the body of the hydranth a monaxonic Archydra, but mouth- 
less and produced by gemmation — with further speculations of the like 
nature. The development of the Medusa of Ohelia flahellata is described, 
with the repeated division of the nucleus and nucleolinus in the 
ova of Ohelia before fertilization, the observations being interpreted as 
indicating that the Hydroid Ohelia under certain conditions is able to 
propagate by spontaneous fission, by a sort of cyst, after the fashion of 
Schizocladium. Red pigment spots in the tips of the arms of Oorrhiza 
are regarded as first indications of organs of sight. The same author 
(17 c) has studied the law of appearance of the tentacles of Hydra : the 
first two tentacles appear at the same time, and are arranged opposite to 
each other, the others also appear in pairs, and are arranged opposite one 
another ; but the second tentacle of each pair always appears later than 
the first, and this retardation is greater in the third pair than in the 
second, and still greater in the fourth. 
Engelmann (10) has repeated Trembley’s celebrated experiments on 
the inversion of Hydra. The result was always negative : if the animal 
did not succeed in speedily retaking its natural position, the Hydra was 
decomposed and rapidly died away, sometimes with the exception of 
the distal portion with the tentacula, which then reproduced a new body. 
Trembley must therefore have deceived himself. Under the same 
circumstances small fragments of tentacles were apt to regenerate whole 
5-armed polypi, individuals divided longitudinally coalesced, &c. 
On the histology of Siphonophora, vide below, p. 16. 
From his researches on the evolution of the generative products in 
Tuhularia and Eudendriuvi, Ciamician (5) concludes that in the last 
genus the spermatozoa are derived from the endoderm, the eggs from 
the ectoderm ; in the former, both from the latter. The formation 
of the spermatozoa in the ectodermal cells of Hydra is confirmed by 
Bbrgh (3), who, in the second part of his paper, gives his observations 
on the identity of the ciliary and amoeboid protoplasmatic motions 
